Tehran University of Medical Sciences Journal of Biostatistics and Epidemiology 2383-4196 7 3 2021 10 23 305 309 Khalil Taherzadeh Chenani Department of Occupational Health Engineering, School of Public Health, Occupational Health Research Center, Yazd, Iran. Farzan Madadizadeh Center for Healthcare Data Modeling, Departments of Biostatistics and Epidemiology, School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. 2021 05 30 2021 07 18 Introduction: Reliability is an integral part of measuring the reproducibility of research information. Intra-cluster correlation coefficient (ICC) is one of the necessary indicators for reliability reporting, which can be misleading in terms of its diversity. The main purpose of this study was to introduce the types of reliability and appropriate ICC indices.  Methods: In this tutorial article, useful information about the types of reliability and indicators needed to report the results, as well as the types of ICC and its applications were explained for dummies.  Results: Three general types of reliability include inter-rater reliability, test-retest reliability, and intra-rater reliability was presented. 10 different types of ICC were also introduced and explained.  Conclusion: The research results may be misleading if any of the reliability types and calculation criteria types are chosen incorrectly. Therefore, to make the results of the study more accurate and valuable. Medical researchers must seek help from relevant guidelines such as this study before conducting reliability analysis. https://jbe.tums.ac.ir/index.php/jbe/article/view/555