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Background: Although nursing intervention studies typically focus on testing hypothesized differences between intervention and control groups, moderator variables can reveal for whom or under what circumstances an intervention may be most effective., Objectives: The aim of the study was to explain and illustrate moderator effects using data from a nursing intervention study to improve cognitive abilities in those with a chronic health condition., Methods: The sample consisted of 178 individuals with multiple sclerosis participating in an experimental study of a cognitive intervention. General linear models were used for analyses. Interaction terms were created to represent moderator effects on three outcomes: self-reported cognitive abilities, use of memory strategies, and verbal memory performance., Results: The Charlson comorbidity index significantly moderated the intervention effect on self-perceived cognitive abilities. Years of education significantly moderated the intervention effect on use of memory strategies. Scores on a general self-efficacy measure significantly moderated the intervention effect on the Controlled Verbal Learning Test-Second Edition., Discussion: These analyses highlight the key role that moderator effects can play in nursing research. Although random assignment to groups can control potentially biasing effects of extraneous differences among individuals in intervention and control groups, those very differences may suggest fruitful avenues for hypothesis generating research about what works best for whom in intervention studies.

Background: Sample sizes set on the basis of desired power and expected effect size are often too small to yield a confidence interval narrow enough to provide a precise estimate of a population value., Approach: Formulae are presented to achieve a confidence interval of desired width for four common statistical tests: finding the population value of a correlation coefficient (Pearson r), the mean difference between two populations (independent- and dependent-samples t tests), and the difference between proportions for two populations (chi-square for contingency tables)., Discussion: Use of the formulae is discussed in the context of the two goals of research: (a) determining whether an effect exists and (b) determining how large the effect is. In addition, calculating the sample size needed to find a confidence interval that captures the smallest benefit of clinical importance is addressed.

Background: R. M. Baron and D. A. Kenny (1986) defined mediation and described how to perform statistical tests of mediation hypotheses. Their approach to testing mediation has been used extensively in the nursing literature. However, many statisticians have identified problems with the Baron and Kenny approach., Purpose: The aim of this paper is to critically evaluate alternative approaches to testing mediation., Approach: The Baron and Kenny approach and its shortcomings are briefly reviewed. A critical analysis of 17 alternate methods in three categories is then presented: (a)causal steps, (b) difference in coefficients, and (c) product of coefficients. The evaluation focuses on Type I error rate control, power, ease of computation, and versatility of use., Results: Of the methods that control Type I error rate adequately, the joint significance test of [alpha] and [beta], the asymmetric distribution of products test, and the test of the products using the percentile bootstrap method are the most powerful tests of mediation. Of these three, the joint significance test of [alpha] and [beta] is superior due to its computational ease and versatility of use., Discussion: Knowledge development in nursing will benefit from continued research testing mediation models. Nurse researchers could move beyond the Baron and Kenny approach to utilize more robust tests of mediation.

Background: Longitudinal designs are indispensable to the study of change in outcomes over time and have an important role in health, social, and behavioral sciences. However, these designs present statistical challenges particularly related to accounting for the variance and covariance of the repeated measurements on the same participants and to modeling outcomes that are not normally distributed., Objectives: The purpose of this study was to introduce a general methodology for longitudinal designs to address these statistical challenges and to present an example of an analysis conducted with data collected in a randomized clinical trial. In this example, the outcome of interest-monthly health-related out-of-pocket expenses incurred by breast cancer survivors-had a skewed distribution., Methods: Common statistical approaches are for longitudinal analysis using linear and generalized linear mixed models are reviewed, and the discussed methods are applied to analyze monthly health-related out-of-pocket expenses., Discussion: Although standard statistical software is available to conduct longitudinal analyses, training is necessary to understand and to take advantage of the various options available for model fitting. However, knowledge of the basics of the methodology allows assimilation and incorporation into practice of evidence from the numerous studies that use these designs.

Background: Statistical significance is often misinterpreted as proof or scientific evidence of importance. This article addresses the most common statistical reporting error in the biomedical literature, namely, confusing statistical significance with clinical importance., Objective: The aim of this study was to clarify the confusion between statistical significance and clinical importance by providing a historical perspective of significance testing, presenting a correct understanding of the information given by p values and significance testing, and offering recommendations for the correct use and reporting of statistical results., Approach: The correct interpretation of p values and statistical significance is given, and the recommendations provided include a description of the current recommended guidelines for statistical reporting of the size of an effect., Results: This article provides a comprehensive overview of p values and significance testing and an understanding of the need for measures of importance and magnitude in statistical reporting., Discussion: Statistical significance is not an objective measure and does not provide an escape from the requirement for the researcher to think carefully and judge the clinical and practical importance of a study's results.

Background: Although the mental health benefits of physical activity (PA) have been documented in numerous primary studies, anxiety outcomes of interventions to increase PA have not been examined through quantitative synthesis., Objectives: The objective of the study was to integrate extant research about anxiety outcomes from interventions to increase PA among healthy adults., Method: Through an extensive literature search, published and unpublished PA intervention studies with anxiety outcomes were located. In eligible studies, findings were reported from interventions designed to increase PA delivered to healthy adults without anxiety disorders. Data were coded from primary studies. Random-effects meta-analytic procedures were completed. Exploratory moderator analyses using meta-analysis analysis of variance and regression analogues were conducted to determine if report, methods, sample, or intervention characteristics were associated with differences in anxiety outcomes., Results: Data were synthesized across 3,289 participants from 19 eligible reports. The overall mean anxiety effect size (d index) for two-group comparisons was .22 with significant heterogeneity (Q = 32.15). With exploratory moderator analyses, larger anxiety improvement effect sizes were found among studies that included larger samples, used random allocation of participants to treatment and control conditions, targeted only PA behavior instead of multiple health behaviors, included supervised exercise (vs. home-based PA), used moderate- or high-intensity instead of low-intensity PA, and suggested participants exercise at a fitness facility (vs. home) following interventions., Discussion: Some interventions can decrease anxiety symptoms among healthy adults. Exploratory moderator analyses suggest possible directions for future primary research to compare interventions in randomized trials to confirm causal relationships.

Background: Interventions to increase physical activity among adults with chronic illness are intended to improve quality of life and reduce disease complications or slow disease progression., Objective: The aim of this study was to integrate quality-of-life outcomes from primary research studies testing interventions to increase physical activity among adults with chronic illness., Methods: Extensive literature searching strategies were used to locate published and unpublished primary research testing physical activity interventions. Results were coded for studies that had at least 5 participants with chronic illness. Fixed- and random-effects meta-analytic procedures included moderator analyses., Results: Eighty-five samples from 66 reports with 7,291 subjects were synthesized. The mean quality-of-life effect size for two-group comparisons (treatment vs. control) was.11 (higher mean quality-of-life scores for treatment subjects than for control subjects). The treatment group pre-post comparison effect size was.27 for quality of life. Heterogeneity was modest in two-group comparisons. Most design and sample attributes were unrelated to intervention effects on quality of life. Studies that exclusively used supervised center-based exercise reported larger quality-of-life improvements than did studies that included any educational/motivational content. Effect sizes were larger among unpublished and unfunded studies. The effect size for physical activity did not predict the quality-of-life effect size., Discussion: Subjects experience improved quality of life from exposure to interventions designed to increase physical activity, despite considerable heterogeneity in the magnitude of the effect. Future primary research should include quality-of-life outcomes so that patterns of relationships among variables can be explored further.

Background: Experimental research in nursing has increased considerably in recent years. To improve the quality of such research, it is critical to reduce threats to internal validity. One threat that has received inadequate attention in the nursing literature is Simpson's paradox--a case of extreme confounding that can lead to erroneous conclusions about the effects of an experimental intervention. In fact, it can lead to a conclusion about an intervention effect that is the opposite of the correct inference., Approach: The aims of this study were to describe Simpson's paradox, provide a hypothetical example, and discuss approaches to avoiding the paradox., Results: The paradox is due to the combination of an overlooked confounding variable and a disproportionate allocation of that variable among experimental groups. Different designs and analysis approaches that can be used to avoid the paradox are presented., Discussion: Simpson's paradox can be avoided by selecting an appropriate experimental design and analysis that incorporates the confounding variable in such a way as to obtain unconfounded estimates of treatment effects, thus more accurately answering the research question.

Background: Statistical mediation is an important tool in behavioral health sciences, but it has been confined primarily to continuous variables. As prevention studies become increasingly common, more often the mediator or outcome is binary. Recent work by D. P. MacKinnon and J. H. Dwyer (1993) has explicated the steps necessary to estimate models for mediation when the mediator or the outcome is binary., Objective: To report the release of a set of SAS macros used to implement the statistical analyses required to analyze data with binary and continuous-level data., Approach: A brief introduction to the methodology of mediation analysis in the presence of a binary outcome, mediator, or both is provided. The macros are tested on a sample of 84 participants who were experiencing pain. It is hypothesized that the relationship between pain and fatigue is mediated by sleep disturbance., Results: The relationship between pain and fatigue was mediated by the presence of sleep disturbances, and the amount of mediation was 23.34%., Discussion: The SAS macros are available for download without charge from the second author's Web site. Instructions are provided in an included technical manual.

Background: Co-bedding, a developmental care practice for twins and multiples, has been theorized as a strategy to decrease the adverse neurodevelopmental effects that may be associated with hospitalization., Objective: The aim of this study was to determine the feasibility of study design, methods, and the measurement of desired outcomes for the development of a larger multicentered study., Results: Study findings were used to estimate effect size, determine staff and bedside care organization, evaluate feasibility of data collection measures, and identify issues related to recruitment and follow-up. Results were incorporated in the development of a larger multicentered trial grant proposal., Discussion: Pilot studies can play an important role in the development of a competitive grant proposal and efficient conduct of a research trial. Pilot studies strengthen a proposal by providing essential baseline information. A general overview of the purpose of pilot studies is provided here, along with a description of the process of using findings from a pilot study to inform the development of a larger multisite trial. Findings from this pilot study examining the effects of co-bedding on twins and their parents are used to revise the research protocol for a larger multisite trial. These changes, which lead to improvement to the protocol, and the rational for these changes are highlighted.

Background: Measurement of health-related quality of life (QOL) over time often yields results that may be difficult to understand. Patients may change their internal standards of QOL as a result of adaptation to deteriorating health, a phenomenon referred to as response shift., Objectives: To examine changes in internal standards of fatigue, global health/QOL, and physical function in patients with inoperable lung cancer at 3 months (n = 115) and 6 months (n = 89) after a baseline measurement close to diagnosis. Significant changes were expected to occur only in patients who reported improvement or deterioration in fatigue and global health/QOL., Methods: Fatigue, global health/QOL, and physical function were assessed with the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC-QLQ-C30, version 3.0). At follow-up, this questionnaire was administered conventionally and as a retrospective baseline assessment (thentest). Subjective transition questions were used to form mutually exclusive patient subgroups (i.e., deterioration, stable, or improvement)., Results: With respect to fatigue, significant changes occurred in patients reporting deterioration at 3 months follow-up and in patients reporting improvement after 6 months, but not in patients reporting improvement after 3 months or deterioration after 6 months. Significant changes in global health/QOL were found in patients reporting improvement at both 3 and 6 months follow-up and unexpectedly in stable patients after 3 months. No significant changes were found in patients reporting deteriorated global health/QOL at 3 and 6 months. Unexpectedly, changes occurred at both 3 and 6 months in patients reporting improved physical function., Discussion: Given these mixed findings, it cannot be concluded that changes in internal standards occurred. These severely ill patients reported high levels of symptoms at baseline and may in part have adapted to their symptoms before study entry.

Background: Although many hospital-based case management (CM) interventions have been studied, there is little work summarizing the effectiveness of these studies., Objectives: The purpose of this study was to investigate the effect of hospital-based CM compared with usual care on length of hospital stay and readmission rate., Method: A meta-analytic method was employed to analyze the effect sizes of CM intervention on outcomes. Eligible studies were retrieved using computerized database searches, footnote chasing, and contact with content experts. The authors reviewed the final 12 studies, and the effect size, 95% confidence interval (CI), sensitivity, homogeneity, and publication bias were analyzed., Results: The overall average weighted effect size on length of stay (LOS) was 0.094 with a 95% CI of -0.032 to 0.220. The overall odds ratio for readmission was 0.87 with a 95% CI of 0.69 to 1.04. Overall, hospital-based CM interventions were not significantly effective in reducing LOS and readmissions. However, CM for patients with heart failure (effect size of 0.241 with a 95% CI of 0.012 to 0.470) was significantly effective in reducing LOS, although it was not effective for stroke patients (effect size of -0.226 with a 95% CI of -0.542 to 0.089) and frail elders (effect size of 0.126 with a 95% CI of -0.073 to 0.324). Analysis indicated that in this meta-analysis publication bias was unlikely., Discussion: The findings of this meta-analysis demonstrate a 6% decrease in readmission rate for patients who received hospital-based CM interventions. Further meta-analytic studies are needed to investigate the effectiveness of CM on other outcomes.

Background: Mediation modeling can explain the nature of the relation among three or more variables. In addition, it can be used to show how a variable mediates the relation between levels of intervention and outcome. The Sobel test, developed in 1990, provides a statistical method for determining the influence of a mediator on an intervention or outcome. Although interactive Web-based and stand-alone methods exist for computing the Sobel test, SPSS and SAS programs that automatically run the required regression analyses and computations increase the accessibility of mediation modeling to nursing researchers., Objectives: To illustrate the utility of the Sobel test and to make this programming available to the Nursing Research audience in both SAS and SPSS., Methods: The history, logic, and technical aspects of mediation testing are introduced. The syntax files sobel.sps and sobel.sas, created to automate the computation of the regression analysis and test statistic, are available from the corresponding author., Results: The reported programming allows the user to complete mediation testing with the user's own data in a single-step fashion. A technical manual included with the programming provides instruction on program use and interpretation of the output., Conclusion: Mediation modeling is a useful tool for describing the relation between three or more variables. Programming and manuals for using this model are made available.

Background: The eutectic mixture of local anesthetics (EMLA), by producing dermal anesthesia through contact with intact skin, has become a major indication for the reduction of pain experienced during venipuncture (VE) and intravenous (IV) insertion., Objectives: The purpose of the study was to determine the mean effect sizes and moderators of EMLA cream application in reducing VE and IV insertion pain., Method: A meta-analysis of 20 studies was conducted to determine the magnitude of the effect of EMLA cream on VE and IV insertion pain. Effect sizes were calculated three ways: weighted, unweighted, and weighted by quality index score. Potential moderating variables of sample age, premedication, therapist control, insertion site, application duration, research design, pain scale, and funding, were investigated for their influence on EMLA's effect., Results: EMLA cream had a large significant effect on VE pain (d = 1.05) with a 95% confidence interval from.92 to 1.34 and a large significant effect on IV insertion pain (d = 1.04) with a 95% confidence interval from.84 to 1.46. Subject age (child versus adult), type of pain scale, number of therapists, location of insertion site, premedication, funding, or study design did not appear to act as effect modifiers., Conclusions: EMLA cream can significantly decrease VE and IV insertion pain in 85% of the population.

Background: Approximately 13% of women experience postpartum depression. Early recognition is one of the most difficult challenges with this mood disorder because of how covertly it is suffered., Objectives: The purpose of this meta-analysis was to update the findings of an earlier meta-analysis of postpartum depression predictors that had synthesized the results of studies conducted mostly in the 1980s., Method: A meta-analysis of 84 studies published in the decade of the 1990s was conducted to determine the magnitude of the relationships between postpartum depression and various risk factors. Using the software system Advanced Basic Meta-Analysis, effect sizes were calculated three ways: unweighted, weighted by sample size, and weighted by quality index score., Results: Thirteen significant predictors of postpartum depression were revealed. Ten of the 13 risk factors had moderate effect sizes while three predictors had small effect sizes. The mean effect size indicator ranges for each risk factor were as follows: prenatal depression (.44 to .46), self esteem (.45 to. 47), childcare stress (.45 to .46), prenatal anxiety (.41 to .45), life stress (.38 to .40), social support (.36 to .41), marital relationship (.38 to .39), history of previous depression (.38 to .39), infant temperament (.33 to .34), maternity blues (.25 to .31), marital status (.21 to .35), socioeconomic status (.19 to .22), and unplanned/unwanted pregnancy (.14 to .17)., Conclusions: Results confirmed findings of an earlier meta-analysis and in addition revealed four new predictors of postpartum depression: self-esteem, marital status, socioeconomic status, and unplanned/unwanted pregnancy.

Background: It is difficult to determine the usefulness of distraction to decrease children's distress behavior and pain during medical procedures because many studies use very small samples and report inconsistent findings., Objectives: To investigate the mean effect sizes across studies for the effects of distraction on young children's distress behavior and self-reported pain during medical procedures., Method: Hunter and Schmidt's (1990) procedures were used to analyze 16 studies (total n = 491) on children's distress behavior and 10 studies (total n = 535) on children's pain., Results: For distress behavior, the mean effect size was 0.33 (+/-0.17), with 74% of the variance accounted for by sampling and measurement error. For pain, the mean effect size was 0.62 (+/-0.42) with 35% of the variance accounted for. Analysis of studies on pain that limited the sample to children 7 years of age or younger (total n = 286) increased the amount of explained variance to 60%., Conclusions: Distraction had a positive effect on children's distress behavior across the populations represented in this study. The effect of distraction on children's self-reported pain is influenced by moderator variables. Controlling for age and type of painful procedure significantly increased the amount of explained variance, but there are other unidentified moderators at work.

This article reports a meta-analysis of 84 studies of quality of life (QOL) in cardiac patient populations published in the 5-year period 1987-1991. Selected methodologies and substantive characteristics of the studies are described. An overall effect size of .31 indicated a small but significant positive effect of pharmacologic, mechanical, surgical, nursing, or other treatment on QOL. No negative effect of treatment was found for any cardiovascular diagnostic category. Homogeneity analysis revealed eight potential moderators of the overall effect size: quality of study, gender of sample, time dimension, sampling method, intervention, marital status of subjects, quality-of-life dimension measured, and sample size.

Gender-related effects and two measures of muscularity, handgrip strength and fat-free mass (FFM), were examined to determine their relationship to respiratory muscle strength. Subjects were 101 healthy older adults. In 75 subjects, the magnitude of learning effect was examined over four weekly sessions. Maximal inspiratory pressure (PImax) was lower with increasing age in women, and maximal expiratory pressure (PEmax) was lower with increasing age in both genders. The PEmax correlated with handgrip strength and FFM in men only. Performance of PImax plateaued by the third visit in both men and women. Performance of PEmax plateaued by the third measure in women and was unchanged across four measurements for men.