multivariate analysis of factors

background: according to the measurements literature reliability of the test refers to the consistency of the test results and shows whether the obtained score is stable indication of the student’s performance in particular test reliability can be measured by different statistics formula. purpose: to determine the factors influenced the reliability of 392 mcq examinations. methods: the correlation of reliabilities of mcq based examination and other characteristics of tests such as length difficult items, discrimination index, mean, standard deviation and time for answering was calculated based on the data available on examination center of tehran university of medical sciences. multivariate regression has been used for data analysis. results: overall reliability of teacher made test is at satisfactory level in most cases. the mean value of reliability was 0.71 ±0.15. in comparing previous semester with last series of examination some improvement have been found during these years (p=0.000, for first semester, p=0.002 for second, p= 0.005 for third and p=0.005 for forth semester). keeping other variable fixed the interaction of length of exam according to item difficulty showedl significant difference on value of test reliability. comparing difficult and easy items question with moderate difficulty index can increase reliability 8 times more than difficult and 13 times more than easy items p=0.000. conclusion: our study showed that with documentation of tests’ metric features an analysis and evaluation of tests are within reach of medical school .