TY - JOUR T1 - Comparison of longitudinal data models for hygroscopic expansion of three common composites TT - مقایسه مدل‌های داده های طولی در انبساط آبی سه کامپوزیت متداول JF - RJMS JO - RJMS VL - 20 IS - 113 UR - http://rjms.iums.ac.ir/article-1-2776-en.html Y1 - 2013 SP - 1 EP - 9 KW - Longitudinal study KW - Marginal model KW - Transition model KW - Multilevel model KW - Hygroscopic expansion. N2 -  Background: Longitudinal studies are widely used in medical and social sciences. According to repeated measurements in these studies, independence assumption is not observed and therefore suitable models should be selected. In this study, application of marginal and transition models for analyzing the longitudinal data related to hygroscopic expansion of composite is shown.  Methods: In this longitudinal study, laboratory data from three common composites (         ,   ) is used. These composites were kept in two different environments (distilled water and natural mouth saliva) for three months and their cylinder length was measured 18 times after preparation of 540 samples. Statistical analysis was done using marginal and transition model and programming with R software. Results: Results show that in marginal model, composite effect was significant (p=0.025, p=0.045) and in transition model, both composite (p M3 ER -