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: Surgery
[{'content': 'All the following statements concerning meta- analysis are true EXCEPT. \nSelect and explain. \nA. It is a study in which the units of analysis are populations or groups of people, rather than individuals., B. It is used to enhance the statistical power of research findings where number in available studies are too small, C. It is applied by pooling results of small, randomized, controlled trials when no single trial has large enough numbers to reach statistical significance, D. It combines results from different studies to obtain a numerical estimate of an overall effect', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Meta-analyses combine results from several studies and, through statistical methods, calculate an overall estimate of effect. Ecological studies use data based on groups of people rather than individuals. Associations observed on an aggregate level may not represent associations on an individual level (ecological bias or ecological fallacy).', 'role': 'assistant'}]