Abstract
The article presents the main methodological principles of planning, implementation and statistical analysis of data from cohort studies. Types of cohort studies, their main advantages and disadvantages, and practical examples of cohort studies in medicine and public health are also presented. We also present the main measures used in cohort studies, namely, the incidence, cumulative incidence, incidence density, absolute risk, relative risk, attributable risk and attributable risk fraction in a given cohort and in a population, incidence rate ratio and incidence rate difference. Examples of cohort studies in literature, including examples from Arkhangelsk region are presented and discussed. The methods of sample size calculation using "EpiInfoTM" software and calculation of the measures of association in cohort studies are also shown using examples from real studies. This is an introductory article about the main methodological principles of cohort study design in health sciences and it does not substitute specialized literature in clinical epidemiology.