Journal of School of Public Health and

In large–scale sampling opeartions (e.g. nation-wide health surveys) we always face the problem of non-response item(s) and/or non-response unit(s). In fitting a model to the data we have two groups of variables, namely dependent and independent variables. Non-response may occur for any of these groups of variables. In this paper we assume Y as a categorical dependent variable with three levels, Z and X as independent variables from any kind: scale, categorical, ordinal, etc. We have complete data on the first two variables and we assume that the missing items follow a random pattern (MAR). Then a model is devised based on the likelihood function for the whole data set (including missing values) and estimates of parameters are compared with those obtained by statistical programs such as SPSS, which are only based on completely observed data and ignore units with missing data. Our results show that the likelihood-based model is superior to the standard approach utilized by the software packages. The comparison is made using data on thyriod disease (goiter) obtained by a health survey in Gazvin province.

Background and Aim: The objective of this study was to assess the psychometric properties of the Adolescent Depression Scale (ADS) based on the item-response theory and compare the results with those based on the classic test theory.

Materials and Methods: A total of 750 students (364 males and 386 females) were selected through multistage random clustering (levels proportional to size) and completed a questionnaire comprising 46 questions developed by the investigators.

Results: Results of factor analysis and questions structure showed that the important item-response theory presumptions, namely, unidimensionality and local independence, are contained in ADS. As regards the psychometric characteristics of the questions, results from the two theories were similar, except that the item-response theory provided more valid indices for assessing the questions. Further analysis of the data indicated that the two theories showed close values for internal consistency with regard to psychometric characteristics, such that values of 0.933 and 0.947 were obtained for Alpha Cronbach and marginal validity, respectively. Finally, the normality scores were calculated based on the Item Response Theory with those based on the Classic Test Theory. Ranking the individuals by the two theories showed considerable differences as regards the depression construct continuum, such as a difference of 86, 92, or 93 individuals.

Conclusions: Based on the findings, it can be concluded that the item-response theory models provides a higher number of more exact indices for judgment and making decisions about questions, tests and individual ranking. Therefore, application of the item-response theory for assessment of other educational and psychological constructs is recommended.