This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
Similarity between Cross sectional study design and Ecological study design:- 
Select and explain. 
A. Both studies are done at a point of time, B. Both provide prevalence, C. Both are based on primary data, D. Unit of study is population
A: Both studies are done at a point of time
Answer: A: Both studies are done at a point of time 
Explanation: Cross Sectional Study Ecological Study Both studies are done at a point of time - Done based on primary Data i.e. collected by Investigation himself from House to House. - It provides "Prevalence", so a/K/a Prevalence Study - a/K/a "SNAPSHOT Study". - Done based on Secondary Data i.e. Collected data from records of hospital Data is not collected by Investigator himself. - Used in Nutritional Surveys - Cannot calculate strength of association / prevalence - Unit of Study is population and results are extrapolated projected not on Individuals but on total population. This drawback is known as "Ecological Fallacy".