Practice Test 1

A cross-sectional study surveys 2,000 high school students (ages 14–18) during a single semester to test whether energy drink use is associated with anxiety symptoms. Students complete anonymous questionnaires on weekly energy drink servings, sleep duration, and a validated anxiety scale; school nurses measure resting heart rate once. Results: 29% report at least 3 energy drinks/week; elevated anxiety scores are present in 34% overall, 45% among high users vs 30% among low/nonusers. High users also report shorter sleep and more social media use. Investigators state they cannot determine directionality.

Which bias is most likely to affect the results of this study?

Investigators conduct a case-control study to evaluate whether prior antibiotic exposure is associated with Clostridioides difficile infection (CDI). Cases are 220 hospitalized adults (median age 67) with positive toxin assay and diarrhea. Controls are 220 hospitalized adults on the same wards without diarrhea, matched by age and length of stay. Antibiotic exposure in the prior 90 days is abstracted from the electronic medication record. Results: 154/220 (70%) cases vs 110/220 (50%) controls received fluoroquinolones. The team notes that some controls later develop diarrhea after discharge, which is not captured.

What is the most appropriate next step in this study design?