1. What are the three main types of epidemiological studies and what are their advantages and disadvantages? Answer: The three main types of epidemiological studies are descriptive, analytical and experimental. Descriptive studies describe the distribution of a disease or a health outcome in a population, such as the frequency, patterns and trends. They are useful for generating hypotheses and identifying potential risk factors, but they cannot establish causal relationships. Analytical studies compare groups of people with different exposures or characteristics to test hypotheses and determine associations between risk factors and outcomes. They can be observational (such as cohort, case-control or cross-sectional studies) or interventional (such as randomized controlled trials). They are useful for testing causality and evaluating interventions, but they may be affected by confounding, bias or ethical issues. Experimental studies manipulate the exposure or intervention in a controlled setting to measure the effect on the outcome. They are the most rigorous and reliable type of study, but they may not be feasible, ethical or generalizable to real-world settings. 2. What is the difference between incidence and prevalence and how are they calculated? Answer: Incidence is the number of new cases of a disease or a health outcome that occur in a population during a specified period of time. It is calculated by dividing the number of new cases by the population at risk during that time. Prevalence is the proportion of people in a population who have a disease or a health outcome at a given point in time or over a specified period of time. It is calculated by dividing the number of existing cases by the total population during that time. Incidence reflects the risk of developing a disease or a health outcome, while prevalence reflects the burden or impact of a disease or a health outcome in a population.