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Abstract Background This study aims at analyzing Health related quality of life (HRQoL) data on the French general population between 1995 and 2003 using an Item Response Theory (IRT) model. Methods Data concerned 26388 individuals having responded to the SF36 questionnaire in 1995 or in 2003. General Health, Mental Health and Physical Functioning dimensions have been analyzed using a latent regression mixed Partial Credit Model. Differential Item Functioning (DIF) have been searched on each item between age categories, genders, regions of residency, and years of study. Mean and variance of the latent traits have been explained by the same variables, in order to quantify their impact. Results Few DIF have been detected between age categories or genders. The analysis shows already known evolutions for HRQoL data: the decrease with age and the differences between genders with worst values for women. We note differences between regions, with better mean value in Paris, in the West or in the South of France, and worst values in the North and in the East. Last, a decrease of the three studied dimensions is noted between 1995 and 2003. Conclusions This study using IRT model offers several advantages compared to a classical approach based on scores. First, DIF can be taken into account. More, handling of missing data is easy, because IRT models do not required imputation of missing data. Last, analysis using IRT model is more powerful than analysis based on scores, and allow highlighting a most important number of effects.

Abstract Background The potentially serious nature of herpes zoster (HZ) and the long-term complication post-herpetic neuralgia (PHN) are often underestimated. One in four people will contract herpes zoster in their lifetime, with this risk rising markedly after the age of 50 years, and affecting one in two in elderly individuals. Pain is the predominant symptom in all phases of HZ disease, being reported by up to 90% of patients. In the acute phase, pain is usually moderate or severe, with patients ranking HZ pain as more intense than post-surgical or labour pains. Up to 20% of patients with HZ develop PHN, which is moderate-to-severe chronic pain persisting for months or years after the acute phase. We review the available data on the effect of HZ and PHN on patients' quality-of-life. Discussion Findings show that HZ, and particularly PHN, have a major impact on patients' lives across all four health domains - physical, psychological, functional and social. There is a clear correlation between increasing severity of pain and greater interference with daily activities. Non-pain complications such as HZ ophthalmicus can increase the risk of permanent physical impairment. Some elderly individuals may experience a permanent loss of independence after an acute episode of HZ. Current challenges in the management of HZ and PHN are highlighted, including the difficulty in administering antiviral agents before pain becomes established and the limited efficacy of pain treatments in many patients. We discuss the clinical rationale for the HZ vaccine and evidence demonstrating that the vaccine reduces the burden of the disease. The Shingles Prevention Study, conducted among >38,000 people aged ≥60 years old, showed that the HZ vaccine significantly reduces the burden of illness and the incidence of both HZ and PHN. In the entire study population, zoster vaccination reduced the severity of interference of HZ and PHN with activities of daily living by two-thirds, as measured by two questionnaires specific to HZ. Summary A vaccination scheme may positively impact the incidence and course of HZ disease, thereby improving patients' quality-of-life.

Abstract Background Missing items are common in quality of life (QoL) questionnaires and present a challenge for research in this field. The development of sound strategies of replacement and prevention requires accurate knowledge of their type and determinants. Methods We used the 2003 French Decennial Health Survey of a representative sample of the general population -- including 22,620 adult subjects who completed the SF-36 questionnaire-- to test various socio-demographic, health status and QoL variables as potential predictors of missingness. We constructed logistic regression models for each SF-36 item to identify independent predictors and classify them according to Little and Rubin ("missing completely at random", "missing at random" and "missing not at random"). Results The type of missingness was missing at random for half of the items of the SF-36 and missing not at random for the others. None of the items were missing completely at random. Independent predictors of missingness were age, female sex, low scores on the SF-36 subscales and in some cases low educational level, occupation, nationality and poor health status. Conclusion This study of the SF-36 shows that imputation of missing items is necessary and emphasizes several factors for missingness that should be considered in prevention strategies of missing data. Similar methodologies could be applied to item missingness in other QoL questionnaires.