Review Question - QID 210888

A medical student is performing clinical research by analyzing the aggregated data of all patients from a national database. In performing the study, she uses all the data collected from patients who had an appendectomy and analyzes the risk factors that are associated with readmission after discharge. She first excludes some of the data based on previously determined exclusion criteria and then performs analysis on the rest. She performs a multiple regression on all variables and finds that one of the risk factors demonstrates a < 5% probability of being the same between groups. She takes this result and presents it to faculty; however, they respond that the finding is meaningless. Which of the following faults to this study most likely explains why the result was considered meaningless?