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Urban air quality and human health are among the key aspects of future urban planning. In order to address pollutants such as ozone and particulate matter, efforts need to be made to quantify and reduce their concentrations. One important aspect in understanding urban air quality is the influence of urban vegetation which may act as both emitter and sink for trace gases and aerosol particles. In this context, the "Berlin Air quality and Ecosystem Research: Local and long-range Impact of anthropogenic and Natural hydrocarbons 2014" (BAERLIN2014) campaign was conducted between 2 June and 29 August in the metropolitan area of Berlin and Brandenburg, Germany. The predominant goals of the campaign were (1) the characterization of urban gaseous and particulate pollution and its attribution to anthropogenic and natural sources in the region of interest, especially considering the connection between biogenic volatile organic compounds and particulates and ozone; (2) the quantification of the impact of urban vegetation on organic trace gas levels and the presence of oxidants such as ozone; and (3) to explain the local heterogeneity of pollutants by defining the distribution of sources and sinks relevant for the interpretation of model simulations. In order to do so, the campaign included stationary measurements at urban background station and mobile observations carried out from bicycle, van and airborne platforms. This paper provides an overview of the mobile measurements (Mobile BAERLIN2014) and general conclusions drawn from the analysis. Bicycle measurements showed micro-scale variations of temperature and particulate matter, displaying a substantial reduction of mean temperatures and particulate levels in the proximity of vegetated areas compared to typical urban residential area (background) measurements. Van measurements extended the area covered by bicycle observations and included continuous measurements of O3, NOx, CO, CO2 and point-wise measurement of volatile organic compounds (VOCs) at representative sites for traffic- and vegetation-affected sites. The quantification displayed notable horizontal heterogeneity of the short-lived gases and particle number concentrations. For example, baseline concentrations of the traffic-related chemical species CO and NO varied on average by up to ±22.2 and ±63.5 %, respectively, on the scale of 100 m around any measurement location. Airborne observations revealed the dominant source of elevated urban particulate number and mass concentrations being local, i.e., not being caused by long-range transport. Surface-based observations related these two parameters predominantly to traffic sources. Vegetated areas lowered the pollutant concentrations substantially with ozone being reduced most by coniferous forests, which is most likely caused by their reactive biogenic VOC emissions. With respect to the overall potential to reduce air pollutant levels, forests were found to result in the largest decrease, followed by parks and facilities for sports and leisure. Surface temperature was generally 0.6–2.1 °C lower in vegetated regions, which in turn will have an impact on tropospheric chemical processes. Based on our findings, effective future mitigation activities to provide a more sustainable and healthier urban environment should focus predominantly on reducing fossil-fuel emissions from traffic as well as on increasing vegetated areas.

Background: Men who suffer recurrence of bulbar urethral stricture have to decide between endoscopic urethrotomy and open urethroplasty to manage their urinary symptoms. Evidence of relative clinical effectiveness and cost-effectiveness is lacking., Objectives: To assess benefit, harms and cost-effectiveness of open urethroplasty compared with endoscopic urethrotomy as treatment for recurrent urethral stricture in men., Design: Parallel-group, open-label, patient-randomised trial of allocated intervention with 6-monthly follow-ups over 24 months. Target sample size was 210 participants providing outcome data. Participants, clinicians and local research staff could not be blinded to allocation. Central trial staff were blinded when needed., Setting: UK NHS with recruitment from 38 hospital sites., Participants: A total of 222 men requiring operative treatment for recurrence of bulbar urethral stricture who had received at least one previous intervention for stricture., Interventions: A centralised randomisation system using random blocks allocated participants 1 : 1 to open urethroplasty (experimental group) or endoscopic urethrotomy (control group)., Main Outcome Measures: The primary clinical outcome was control of urinary symptoms. Cost-effectiveness was assessed by cost per quality-adjusted life-year (QALY) gained over 24 months. The main secondary outcome was the need for reintervention for stricture recurrence., Results: The mean difference in the area under the curve of repeated measurement of voiding symptoms scored from 0 (no symptoms) to 24 (severe symptoms) between the two groups was -0.36 [95% confidence interval (CI) -1.78 to 1.02; p  = 0.6]. Mean voiding symptom scores improved between baseline and 24 months after randomisation from 13.4 [standard deviation (SD) 4.5] to 6 (SD 5.5) for urethroplasty group and from 13.2 (SD 4.7) to 6.4 (SD 5.3) for urethrotomy. Reintervention was less frequent and occurred earlier in the urethroplasty group (hazard ratio 0.52, 95% CI 0.31 to 0.89; p  = 0.02). There were two postoperative complications requiring reinterventions in the group that received urethroplasty and five, including one death from pulmonary embolism, in the group that received urethrotomy. Over 24 months, urethroplasty cost on average more than urethrotomy (cost difference £2148, 95% CI £689 to £3606) and resulted in a similar number of QALYs (QALY difference -0.01, 95% CI -0.17 to 0.14). Therefore, based on current evidence, urethrotomy is considered to be cost-effective., Limitations: We were able to include only 69 (63%) of the 109 men allocated to urethroplasty and 90 (80%) of the 113 men allocated to urethrotomy in the primary complete-case intention-to-treat analysis., Conclusions: The similar magnitude of symptom improvement seen for the two procedures over 24 months of follow-up shows that both provide effective symptom control. The lower likelihood of further intervention favours urethroplasty, but this had a higher cost over the 24 months of follow-up and was unlikely to be considered cost-effective., Future Work: Formulate methods to incorporate short-term disutility data into cost-effectiveness analysis. Survey pathways of care for men with urethral stricture, including the use of enhanced recovery after urethroplasty. Establish a pragmatic follow-up schedule to allow national audit of outcomes following urethral surgery with linkage to NHS Hospital Episode Statistics., Trial Registration: Current Controlled Trials ISRCTN98009168., Funding: This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment ; Vol. 24, No. 61. See the NIHR Journals Library website for further project information.

Background: Urethral stricture affects 0.9% of men. Initial treatment is urethrotomy. Approximately, half of the strictures recur within 4 yr. Options for further treatment are repeat urethrotomy or open urethroplasty., Objective: To compare the effectiveness and cost-effectiveness of urethrotomy with open urethroplasty in adult men with recurrent bulbar urethral stricture., Design, Setting, and Participants: This was an open label, two-arm, patient-randomised controlled trial. UK National Health Service hospitals were recruited and 222 men were randomised to receive urethroplasty or urethrotomy., Intervention: Urethrotomy is a minimally invasive technique whereby the narrowed area is progressively widened by cutting the scar tissue with a steel blade mounted on a urethroscope. Urethroplasty is a more invasive surgery to reconstruct the narrowed area., Outcome Measurements and Statistical Analysis: The primary outcome was the profile over 24 mo of a patient-reported outcome measure, the voiding symptom score. The main clinical outcome was time until reintervention., Results and Limitations: The primary analysis included 69 (63%) and 90 (81%) of those allocated to urethroplasty and urethrotomy, respectively. The mean difference between the urethroplasty and urethrotomy groups was -0.36 (95% confidence interval [CI] -1.74 to 1.02). Fifteen men allocated to urethroplasty needed a reintervention compared with 29 allocated to urethrotomy (hazard ratio [95% CI] 0.52 [0.31-0.89])., Conclusions: In men with recurrent bulbar urethral stricture, both urethroplasty and urethrotomy improved voiding symptoms. The benefit lasted longer for urethroplasty., Patient Summary: There was uncertainty about the best treatment for men with recurrent bulbar urethral stricture. We randomised men to receive one of the following two treatment options: urethrotomy and urethroplasty. At the end of the study, both treatments resulted in similar and better symptom scores. However, the urethroplasty group had fewer reinterventions., (Copyright © 2020. Published by Elsevier B.V.)

Diabetes self-management education and support (DSME/S) has been demonstrated as an effective intervention and a billable service; however, DSME/S has yet to be successfully translated and diffused into mainstream practice. This project sought to improve glycemic control (measured by A1C or fasting blood glucose [FBG]) and quality of life (QOL) of Medicare patients age 65 years and older with type 2 diabetes (T2DM) using DSME/S. DSME/S included information sharing between patients and providers, psychosocial support, behavioral support with lifestyle modification, multi-disciplinary integration, and care coordination. Patient-specific data were compared before and 4 weeks after project implementation. Use of DSME/S increased by 15% (p < .005). Participants demonstrated a statistically significant decrease in mean FBG and a statistically significant increase in QOL. This project demonstrated the successful translation of evidence related to DSME/S into practice through improving diabetes care and promoting continuing education for all of the providers. [J Contin Educ Nurs. 2020;51(3):119-123.]., (Copyright 2020, SLACK Incorporated.)

Many assessment scales in the social sciences are composed of multiple items that form a subscale structure. They have this structure because more than one aspect of the variable is assessed and more than one item assesses each aspect. Nevertheless, generally, a single measurement is required from the scale. A characteristic of this measurement is that the greater the number of items, and categories within an item, that assess an aspect, the greater its influence on the final measurement. One way to control this influence is to include the desired relative number of items and categories to assess each aspect in the scale. However, there are circumstances where designing the required number of items and categories for each aspect is challenging. This paper shows a method of controlling the influence of the number of items and categories assessing each aspect by a-priori weighting of items at the person measurement stage with the Rasch model.

The pair comparison design for distinguishing between stimuli located on the same natural or hypothesized linear continuum is used both when the response is a personal preference and when it is an impersonal judgment. Appropriate models which complement the different responses have been proposed. However, the models most appropriate for impersonal judgments have also been described as modeling choice, which may imply personal preference. This leads to potential confusion in interpretation of scale estimates of the stimuli, in particular whether they reflect a substantive order on the variable or reflect a characteristic of the sample which is different from the substantive order on the variable. Using Thurstone's concept of a discriminal response when a person engages with each stimulus, this article explains the overlapping and distinctive relationships between models for pair comparison designs when used for preference and judgment. In doing so, it exploits the properties of the relatively new hyperbolic cosine model which is not only appropriate for modeling personal preferences but has an explicit mathematical relationship with models for impersonal judgments. The hyperbolic cosine model is shown to be a special case of a more general form, referred to in parallel with Thurstone's Law of Comparative Judgment, as a specific law of comparative preference . Analyses of two real data sets illustrate the differences between the models most appropriate for personal preferences and impersonal judgments in a pair comparison design., Competing Interests: Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

The advantages of using person location estimates from the Rasch model over raw scores for the measurement of change using a common test include the linearization of scores and the automatic handling of statistical properties of repeated measurements. However, the application of the model requires that the responses to the items are statistically independent in the sense that the specific responses to the items on the first time of testing do not affect the responses at a second time. This requirement implies that the responses to the items at both times of assessment are governed only by the invariant location parameters of the items at the two times of testing and the location parameters of each person each time. A specific form of dependence that is pertinent when the same items are used is when the observed response to an item at the second time of testing is affected by the response to the same item at the first time, a form of dependence which has been referred to as response dependence. This paper presents the logic of applying the Rasch model to quantify, control and remove the effect of response dependence in the measurement of change when the same items are used on two occasions. The logic is illustrated with four sets of simulation studies with dichotomous items and with a small example of real data. It is shown that the presence of response dependence can reduce the evidence of change, a reduction which may impact interpretations at the individual, research, and policy levels.

The possibility that the validity of assessment is compromised by repeated sittings of highly competitive and high profile selection tests has been documented and is of concern to stake-holders. An illustrative example is the Undergraduate Medicine and Health Sciences Admission Test (UMAT) used by some medical and dental courses in Australia and New Zealand. The proficiencies of all applicants who sat the UMAT from one to four sittings between 2006 and 2012 were estimated on the same metric using the probabilistic Rasch model. A fit index characterising each profile's degree of conformity to the model was also calculated. Confirming expectations, mean proficiencies increased with repeated sittings on all three UMAT scales with the greatest difference (which was nevertheless relatively small) between the first two sittings. The fit index showed that the increases in proficiency estimates arose from additional easier items being answered correctly on repeated sittings rather than additional more difficult ones, suggesting that improvements are not on the substantive construct of the variable of assessment but in skills in answering the questions. Although strategies for dealing with the increase in proficiency estimates on repeated sittings could be canvassed, these results suggest that the validity of results on repeated sittings was not compromised. Accordingly, it might be concluded that although particular individuals might improve substantially between sittings, any validity is not likely to be compromised with the possibility that for some applicants, the second sitting might be the most valid.

Background: Rasch analysis with a focus on Differential Item Functioning (DIF) is increasingly used for examination of psychometric properties of health outcome measures. To take account of DIF in order to retain precision of measurement, split of DIF-items into separate sample specific items has become a frequently used technique. The purpose of the paper is to present and summarise recent advances of analysis of DIF in a unified methodology. In particular, the paper focuses on the use of analysis of variance (ANOVA) as a method to simultaneously detect uniform and non-uniform DIF, the need to distinguish between real and artificial DIF and the trade-off between reliability and validity. An illustrative example from health research is used to demonstrate how DIF, in this case between genders, can be identified, quantified and under specific circumstances accounted for using the Rasch model., Methods: Rasch analyses of DIF were conducted of a composite measure of psychosomatic problems using Swedish data from the Health Behaviour in School-aged Children study for grade 9 students collected during the 1985-2014 time periods., Results: The procedures demonstrate how DIF can be identified efficiently by ANOVA of residuals, and how the magnitude of DIF can be quantified and potentially accounted for by resolving items according to identifiable groups and using principles of test equating on the resolved items. The results of the analysis also show that the real DIF in some items does affect person measurement estimates., Conclusions: Firstly, in order to distinguish between real and artificial DIF, the items showing DIF initially should not be resolved simultaneously but sequentially. Secondly, while resolving instead of deleting a DIF item may retain reliability, both options may affect the content validity negatively. Resolving items with DIF is not justified if the source of the DIF is relevant for the content of the variable; then resolving DIF may deteriorate the validity of the instrument. Generally, decisions on resolving items to deal with DIF should also rely on external information.

The standard treatment of bulbar urethral strictures of appropriate length is excision and primary anastomosis (EPA), irrespective of the cause of the stricture. This involves transection of the corpus spongiosum (CS) and disruption of the blood flow within the CS as a consequence. The success rate of EPA in curing these strictures is very high, but there is a considerable body of evidence and of opinion to suggest that there is a significant risk of sexual dysfunction and, potentially, of other adverse consequences that occur because of transection of the CS., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Purpose: Rectourethral fistula is a known complication of prostate cancer treatment. Reports in the literature on rectourethral fistula repair technique and outcomes are limited to single institution series. We examined the variations in technique and outcomes of rectourethral fistula repair in a multi-institutional setting., Materials and Methods: We retrospectively identified patients who underwent rectourethral fistula repair after prostate cancer treatment at 1 of 4 large volume reconstructive urology centers, including University of California-San Francisco, University College London Hospitals, Lahey Clinic and Devine-Jordan Center for Reconstructive Surgery, in a 15-year period. We examined the types of prostate cancer treatment, technical aspects of rectourethral fistula repair and outcomes., Results: After prostate cancer treatment 201 patients underwent rectourethral fistula repair. The fistula developed in 97 men (48.2%) after radical prostatectomy alone and in 104 (51.8%) who received a form of energy ablation. In the ablation group 84% of patients underwent bowel diversion before rectourethral fistula repair compared to 65% in the prostatectomy group. An interposition flap or graft was placed in 91% and 92% of the 2 groups, respectively. Concomitant bladder neck contracture or urethral stricture developed in 26% of patients in the ablation group and in 14% in the prostatectomy group. Postoperatively the rates of urinary incontinence and complications were higher in the energy ablation group at 35% and 25% vs 16% and 11%, respectively. The ultimate success rate of fistula repair in the energy ablation and radical prostatectomy groups was 87% and 99% with 92% overall success., Conclusions: Rectourethral fistulas due to prostate cancer therapy can be reconstructed successfully in a high percent of patients. This avoids permanent urinary diversion in these complex cases., (Copyright © 2017 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.)

This article reproduces correspondence between Georg Rasch of The University of Copenhagen and Benjamin Wright of The University of Chicago in the period from January 1966 to July 1967. This correspondence reveals their struggle to operationalize a unidimensional measurement model with sufficient statistics for responses in a set of ordered categories. The article then explains the original approach taken by Rasch, Wright, and Andersen, and then how, from a different tack originating in 1961 and culminating in 1978, three distinct stages of development led to the current relatively simple and elegant form of the model. The article shows that over this period of almost two decades, the demand for sufficiency of a unidimensional parameter of the object of measurement, which enabled the separation of this parameter from the parameter of the instrument, drove the theoretical development of the model., Competing Interests: Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Recent research has shown how the statistical bias in Rasch model difficulty estimates induced by guessing in multiple-choice items can be eliminated. Using vertical scaling of a high-profile national reading test, it is shown that the dominant effect of removing such bias is a nonlinear change in the unit of scale across the continuum. The consequence is that the proficiencies of the more proficient students are increased relative to those of the less proficient. Not controlling the guessing bias underestimates the progress of students across 7 years of schooling with important educational implications., Competing Interests: Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Test theories imply statistical, local independence. Where local independence is violated, models of modern test theory that account for it have been proposed. One violation of local independence occurs when the response to one item governs the response to a subsequent item. Expanding on a formulation of this kind of violation between two items in the dichotomous Rasch model, this paper derives three related implications. First, it formalises how the polytomous Rasch model for an item constituted by summing the scores of the dependent items absorbs the dependence in its threshold structure. Second, it shows that as a consequence the unit when the dependence is accounted for is not the same as if the items had no response dependence. Third, it explains the paradox, known, but not explained in the literature, that the greater the dependence of the constituent items the greater the apparent information in the constituted polytomous item when it should provide less information.

Contains a correction to Table 5 in original publication appearing in Journal of Applied Measurement, 17, 262-282.

Differential item functioning (DIF) for an item between two groups is present if, for the same person location on a variable, persons from different groups have different expected values for their responses. Applying only to dichotomously scored items in the popular Mantel-Haenszel (MH) method for detecting DIF in which persons are classified by their total scores on an instrument, Andrich and Hagquist articulated the concept of artificial DIF and showed that as an artifact of the MH method, real DIF in one item favoring one group inevitably induces artificial DIF favoring the other group in all other items. Using the dichotomous Rasch model in which the total score for a person is a sufficient statistic, and therefore justifies classifying persons by their total scores, Andrich and Hagquist showed that to distinguish between real and artificial DIF in an item identified by the MH method, a sequential procedure for resolving items is implied. Using the polytomous Rasch model, this article generalizes the concept of artificial DIF to polytomous items, in which multiple item parameters play a role. The article shows that the same principle of resolving items sequentially as with dichotomous items applies also to distinguishing between real and artificial DIF with polytomous items. A real example and a small simulated example that parallels the real example are used illustratively., Competing Interests: Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Background: The UMAT is widely used for selection into undergraduate medical and dental courses in Australia and New Zealand (NZ). It tests aptitudes thought to be especially relevant to medical studies and consists of 3 sections - logical reasoning and problem solving (UMAT-1), understanding people (UMAT-2) and non-verbal reasoning (UMAT-3). A substantial proportion of all candidates re-sit the UMAT. Re-sitting raises the issue as to what might be the precise magnitude and determinants of any practice effects on the UMAT and their implications for equity in subsequent selection processes., Methods: Between 2000 and 2012, 158,909 UMAT assessments were completed. From these, 135,833 cases were identified where a candidate had sat once or more during that period with 117,505 cases (86.5%) having sat once, 14,739 having sat twice (10.9%), 2,752 thrice (2%) and 837, 4 or more times (0.6%). Subsequent analyses determined predictors of multiple re-sits as well as the magnitude and socio-demographic determinants of any practice effects., Results: Increased likelihood of re-sitting the UMAT twice or more was predicted by being male, of younger age, being from a non-English language speaking background and being from NZ and for Australian candidates, being urban rather than rurally based. For those who sat at least twice, the total UMAT score between a first and second attempt improved by 10.7 ± 0.2 percentiles, UMAT-1 by 8.3 ± 0.2 percentiles, UMAT-2 by 8.3 ± 0.2 percentiles and UMAT-3 by 7.7 ± 0.2 percentiles. An increase in total UMAT percentile score on re-testing was predicted by a lower initial score and being a candidate from NZ rather than from Australia while a decrease was related to increased length of time since initially sitting the test, older age and non-English language background., Conclusions: Re-sitting the UMAT augments performance in each of its components together with the total UMAT percentile score. Whether this increase represents just an improvement in performance or an improvement in understanding of the variables and therefore competence needs to be further defined. If only the former, then practice effects may be introducing inequity in student selection for medical or dental schools in Australia or NZ.

In this systematic review of the literature, a search of the PubMed database was conducted to identify articles dealing with augmentation/substitution urethral reconstruction of the anterior urethral stricture. The evidence was categorized by stricture site, surgical technique, and the type of tissue used. The committee appointed by the International Consultation on Urological Disease reviewed this data and produced a consensus statement relating to the augmentation and substitution of the anterior urethra. In this review article, the background pathophysiology is discussed. Most cases of urethral stricture disease in the anterior urethra are consequent on an ischemic spongiofibrosis. The choice of technique and the surgical approach are discussed along with the potential pros and cons of the use of a graft vs a flap. There is research potential for tissue engineering. The efficacy of the surgical approach to the urethra is reviewed. Whenever possible, a 1-stage approach is preferable from the patient's perspective. In some cases, with complex penile urethral strictures, a 2-stage procedure might be appropriate, and there is an important potential role for the use of a perineal urethrostomy in cases where there is an extensive anterior urethral stricture or where the patient does not wish to undergo complex surgery, or medical contraindications make this hazardous. It is important to have accurate outcome measures for the follow-up of patients, and in this context, a full account needs to be taken of patients' perspectives by the use of appropriate patient-reported outcome measures. The use of symptoms and a flow rate can be misleading. It is well established that with a normally functioning bladder, the flow rate does not diminish until the caliber of the urethra falls below 10F. The most accurate means of following up patients after stricture surgery are by the use of endoscopy or visualization by urethrography. Careful consideration needs to be made of the outcomes reported in the world literature, bearing in mind these aforementioned points. The article concludes with an overview of the key recommendations provided by the committee., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Background: The increasing influence of patient-reported outcome (PRO) measurement instruments indicates their scrutiny has never been more crucial. Above all, PRO instruments should be valid: shown to assess what they purport to assess., Objectives: To evaluate a widely used fatigue PRO instrument, highlight key issues in understanding PRO instrument validity, demonstrate limitations of those approaches and justify notable changes in the validation process., Methods: A two-phase evaluation of the 40-item Fatigue Impact scale (FIS): a qualitative evaluation of content and face validity using expert opinion (n=30) and a modified Delphi technique; a quantitative psychometric evaluation of internal and external construct validity of data from 333 people with multiple sclerosis using traditional and modern methods., Results: Qualitative evaluation did not support content or face validity of the FIS. Expert opinion agreed with the subscale placement of 23 items (58%), and classified all 40 items as being non-specific to fatigue impact. Nevertheless, standard quantitative psychometric evaluations implied, largely, FIS subscales were reliable and valid., Conclusions: Standard quantitative 'psychometric' evaluations of PRO instrument validity can be misleading. Evaluation of existing PRO instruments requires both qualitative and statistical methods. Development of new PRO instruments requires stronger conceptual underpinning, clearer definitions of the substantive variables for measurement and hypothesis-testing experimental designs.

Assessments with ratings in ordered categories have become ubiquitous in health, biological and social sciences. Ratings are used when a measuring instrument of the kind found in the natural sciences is not available to assess some property in terms of degree - for example, greater or smaller, better or worse, or stronger or weaker. The handling of ratings has ranged from the very elementary to the highly sophisticated. In an elementary form, and assumed in classical test theory, the ratings are scored with successive integers and treated as measurements; in a sophisticated form, and used in modern test theory, the ratings are characterized by probabilistic response models with parameters for persons and the rating categories. Within modern test theory, two paradigms, similar in many details but incompatible on crucial points, have emerged. For the purposes of this article, these are termed the statistical modeling and experimental measurement paradigms. Rather than reviewing a compendium of available methods and models for analyzing ratings in detail, the article focuses on the incompatible differences between these two paradigms, with implications for choice of model and inferences. It shows that the differences have implications for different roles for substantive researchers and psychometricians in designing instruments with rating scales. To illustrate these differences, an example is provided.

There is a substantial literature on attempts to obtain information on the proficiency of respondents from distractors in multiple choice items. Information in a distractor implies that a person who chooses that distractor has greater proficiency than if the person chose another distractor with no information. A further implication is that the distractor deserves partial credit. However, it immediately follows from the Rasch model that if a distractor deserves partial credit, then the response to that distractor and other distractors should not be pooled into a single response with a single probability of an incorrect response. Using the partial credit parameterization of the polytomous Rasch model, the paper shows how an hypothesis can be formed, and tested, regarding information in a distractor. The hypothesis is formed by studying the shape of the distractor response curves across the continuum, and the hypothesis is tested by scoring the correct response 2, the hypothesized distractor 1, and other distractors 0, and then applying the polytomous Rasch model. Multiple pieces of evidence, including fit of the responses at the two thresholds and the order of the two threshold estimates, are used in deciding if a distractor has information. An example illustrating the theory and its application is provided.

The 'halo effect' may be unique to different raters or common to all raters. When common to all raters, halo is not detectable through standard fit indices of the three-facet Rasch model used to account for differences in rater severities. Using a formulation of halo as a violation of local independence, a halo effect common to all raters is simulated and shown to be diagnosable through contrasts between two-facet stack and rack Rasch analyses. In the former, the thresholds are clustered and the distribution of persons is multimodal; in the latter, all thresholds are close together and the distribution of persons is unimodal. In the former, the scale is stretched, and the person separation inflated, relative to the latter.

By adding items with responses identical to a selected item, Smith (2005) investigated the effect of the response dependence on person and item parameter estimates in the dichotomous Rasch model. By varying the magnitude of response dependence among selected items, rather than their having perfect dependence, this paper provides additional insights into the effects of response dependence on the same estimates in the same model. Two sets of simulations are reported. In the first set, responses to all items except the first were dependent on either the first item or on the immediately preceding item; in the second set, subsets of items were formed first, and then within each of these subsets, responses to all items in a subset except the first were dependent on either the first item or on the immediately preceding item. The effects of dependence were noticeable in all of the statistics reported. In particular, the fit statistics and the parameter estimates showed increasing discrepancies from their theoretical values as a function of the magnitude of the dependence. In some cases, however, two related statistics gave the impression of improvement as a function of increased dependency; first the standard deviation of person estimates showed an increase, and second the index analogous to traditional reliability showed relative increase. In addition to the estimates and depending on the structure and magnitude of the dependence, the person distribution was affected systematically, ranging from becoming skewed to becoming bimodal. The effects on the distribution help explain some of the effects on the statistics reported. In the case of the second set of simulations in which the dependence is within subsets of items, it is possible to take account of the response dependence. This is done by summing the responses of the items within each subset to form a polytomous item and then analyzing the data in terms of a smaller number of polytomous items. This way of accounting for dependence, in which the maximum score for the test as a whole remains the same, gives a more accurate value of the reliability and a more realistic distribution of the person estimates than when the dependence within subsets of items is not taken into account.

Local independence in the Rasch model can be violated in two generic ways that are generally not distinguished clearly in the literature. In this paper we distinguish between a violation of unidimensionality, which we call trait dependence, and a specific violation of statistical independence, which we call response dependence, both of which violate local independence. Distinct algebraic formulations for trait and response dependence are developed as violations of the dichotomous Rasch model, data are simulated with varying degrees of dependence according to these formulations, and then analysed according to the Rasch model assuming no violations. Relative to the case of no violation it is shown that trait and response dependence result in opposite effects on the unit of scale as manifested in the range and standard deviation of the scale and the standard deviation of person locations. In the case of trait dependence the scale is reduced; in the case of response dependence it is increased. Again, relative to the case of no violation, the two violations also have opposite effects on the person separation index (analogous to Cronbach's alpha reliability index of traditional test theory in value and construction): it decreases for data with trait dependence; it increases for data with response dependence. A standard way of accounting for dependence is to combine the dependent items into a higher-order polytomous item. This typically results in a decreased person separation index index and Cronbach's alpha, compared with analysing items as discrete, independent items. This occurs irrespective of the kind of dependence in the data, and so further contributes to the two violations not being distinguished clearly. In an attempt to begin to distinguish between them statistically this paper articulates the opposite effects of these two violations in the dichotomous Rasch model.

The purpose of this paper is to explain the role of the unit implicit in the dichotomous Rasch model in determining the multiplicative factor of separation between measurements in a specified frame of reference. The explanation is provided at two complementary levels: first, in terms of the algebra of the model in which the role of an implicit, multiplicative constant is made explicit; and second, at a more fundamental level, in terms of the classical definition of measurement in the physical sciences. The Rasch model is characterized by statistical sufficiency, which arises from the requirement of invariant comparisons within a specified frame of reference. A frame of reference is defined by a class of persons responding to a class of items in a well-defined response context. The paper shows that two or more frames of reference may have different implicit units without destroying sufficiency. Understanding the role of the unit permits explication of the relationship between the Rasch model and the two parameter logistic model. The paper also summarises an approach that can be used in practice to express measurements across different frames of reference in the same unit.

Background: As assessment has been shown to direct learning, it is critical that the examinations developed to test clinical competence in medical undergraduates are valid and reliable. The use of extended matching questions (EMQ) has been advocated to overcome some of the criticisms of using multiple-choice questions to test factual and applied knowledge., Methods: We analysed the results from the Extended Matching Questions Examination taken by 4th year undergraduate medical students in the academic year 2001 to 2002. Rasch analysis was used to examine whether the set of questions used in the examination mapped on to a unidimensional scale, the degree of difficulty of questions within and between the various medical and surgical specialties and the pattern of responses within individual questions to assess the impact of the distractor options., Results: Analysis of a subset of items and of the full examination demonstrated internal construct validity and the absence of bias on the majority of questions. Three main patterns of response selection were identified., Conclusion: Modern psychometric methods based upon the work of Rasch provide a useful approach to the calibration and analysis of EMQ undergraduate medical assessments. The approach allows for a formal test of the unidimensionality of the questions and thus the validity of the summed score. Given the metric calibration which follows fit to the model, it also allows for the establishment of items banks to facilitate continuity and equity in exam standards.

A category with a frequency of zero is called a null category. When null categories are present in polytomous responses, then in the Rasch model for such responses, the thresholds that define the categories are inestimable with the commonly used joint maximum likelihood, marginal maximum likelihood, or standard conditional maximum likelihood estimation algorithms. The reason for this situation is that in principle, these estimation algorithms involve frequencies of each category. Andrich and Luo (2003) describe an algorithm in which the thresholds are reparameterized into their principal components and in which the estimate of any threshold is based on a function of the frequencies of all categories of the item rather than the frequency of a particular category. This algorithm works in the presence of null categories. However, in situations where the null categories are at the extremes of a set of categories, the estimates themselves can become too extreme. This paper describes a procedure in which the solution algorithm described by Andrich and Luo is further adapted in the presence of null categories by using their expected frequencies. The procedure is demonstrated with simulated and real data.

The development of Rasch models in educational and psychologic measurement in the 1960s coincided with the introduction of other similar models, now described as models of item response theory (IRT). The application of IRT models has now extended to other social sciences, including health. Originally, there was substantial controversy between those who saw Rasch models as simply special cases of IRT models and those who saw them as essentially different. Because these different perspectives continue to manifest themselves in various ways, it seems relevant to understand the source of the original controversy. This paper attempts to do so by invoking Kuhn's studies in the history and philosophy of science at 3 levels. First, it suggests that the 2 perspectives reflect Kuhn's concept of legitimate, incompatible paradigms in which controversy is a typical manifestation. Second, because Kuhn recognizes individual histories in the development of paradigms, Rasch's own shift in perspective is summarized. Third, because proponents of the Rasch models emphasize the models' compatibility with fundamental measurement found in physical science, an analogy is made between how Kuhn explains the role of measurement in the physical sciences and how proponents of Rasch models explain the role of these models in the social sciences. In particular, these roles cannot be gleaned from textbooks in science and statistics, respectively.

In the Rasch model for items with more than two ordered response categories, the thresholds that define the successive categories are an integral part of the structure of each item in that the probability of the response in any category is a function of all thresholds, not just the thresholds between any two categories. This paper describes a method of estimation for the Rasch model that takes advantage of this structure. In particular, instead of estimating the thresholds directly, it estimates the principal components of the thresholds, from which threshold estimates are then recovered. The principal components are estimated using a pairwise maximum likelihood algorithm which specialises to the well known algorithm for dichotomous items. The method of estimation has three advantageous properties. First, by considering items in all possible pairs, sufficiency in the Rasch model is exploited with the person parameter conditioned out in estimating the item parameters, and by analogy to the pairwise algorithm for dichotomous items, the estimates appear to be consistent, though unlike for the dichotomous case, no formal proof has yet been provided. Second, the estimates of each item parameter is a function of frequencies in all categories of the item rather than just a function of frequencies of two adjacent categories. This stabilizes estimates in the presence of low frequency data. Third, the procedure accounts readily for missing data. All of these properties are important when the model is used for constructing variables from large scale data sets which must account for structurally missing data. A simulation study shows that the quality of the estimates is excellent.

The case for the Rasch models, that The comparison between two stimuli should be independent of which particular individuals were instrumental for the comparison; and vice versa (Rasch, 1961), does not depend on the models accounting for any data set. This has two distinctive consequences on the data-model relationship for the Rasch models. First, and this was recognized by Rasch, when there are deviations of one sort or another, it turns upside down the question of whether it is the model or the test that has gone wrong (Rasch, 1960). Second, because the invariance of comparisons among stimuli, and vice versa, is built into the model rather than being merely a requirement of data, further implications of this requirement can be derived mathematically. These implications, too, inevitably turn some questions, and their solutions, upside down. It is argued that having to look at these implications upside down produces substantial psychological and intellectual resistance amongst those schooled in looking at them in the traditional way. It is also argued that in turning the question upside down, Rasch had an insight that goes beyond the mathematical derivations, and that to sustain this insight requires a paradigm shift (Kuhn, 1970) in the data-model relationship. Using an illustrative example, it is suggested that to maintain this paradigm shift, even by those who research the Rasch models, requires the same uncompromising consistency and passion that Rasch displayed in maintaining faith in his insight.

This study examines the Likert-style successive integer scoring of Goldberg's (1972, 1978) General Health Questionnaire (GHQ) with a psychometric model in which the thresholds between successive categories within each item can be estimated. The model is particularly appropriate because the scoring of the successive categories, which are not named in the same way across items, by successive integers has received substantial discussion in the literature. Results from 1967 teachers in Western Australia who completed the 30-item form of the GHQ show that the items conform reasonably well to the model at a general or macro-level of analysis. In particular, the original ordering of categories is supported. However, as expected, there are systematic differences between distances among threshold within items and systematic differences among thresholds between items. The differences between positively and negatively orientated items confirm a suggestion in the literature that these two classes of items form sufficiently different scales so that they could be treated as separate, though reasonably correlated, scales.