This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
All of the following studies are 'analytical', except: 
Select and explain. 
A. Field trials, B. Coho studies, C. Case control studies, D. Ecological studies
A: Field trials
Answer: A: Field trials 
Explanation: Field trial is a type of experimental or interventional study. Coho study, case control study and ecological study are all types of analytical studies. Ref: Park's Textbook of Preventive and Social Medicine, By K. Park, 19th Edition, Page 58