Epidemiology is the systematic study of the distribution and determinants of health-related conditions or events in specified populations and the application of this knowledge to control health problems. It is an important discipline of public health because it helps identify the frequency, causes, risk factors and patterns of diseases in communities. Epidemiologists study who develops a disease, where it occurs, when it occurs and why it occurs. The information obtained through epidemiological studies is used for disease prevention, health promotion, planning of health services and evaluation of public health interventions. Epidemiological studies are broadly classified into observational and experimental studies. Randomised studies are a major type of experimental or intervention study. In a randomised study, participants are assigned to different groups by a process of random allocation. Usually, one group receives the intervention being studied, while another group serves as a control and receives a standard treatment, placebo or no intervention. Randomisation ensures that each participant has an equal or known chance of being allocated to any study group. The most important form of