Study Design Classification
This is a cohort study (Answer A) when comparing health outcomes between groups defined by different TV watching habits (2 hours daily vs. no TV watching).
Reasoning Based on Study Design Characteristics
Why This is a Cohort Study
A cohort study follows groups of individuals defined by their exposure status forward in time to assess outcomes. 1, 2 In this scenario:
- Group A (exposed): Watches TV for 2 hours daily
- Group B (unexposed): Does not watch TV
- The groups are defined by their exposure status (TV watching behavior) before outcomes are measured 3
- Participants are then followed to observe health outcomes that develop over time 4, 5
Key Distinguishing Features
Cohort studies select participants based on exposure status, not outcome status. 2, 3 This is the critical distinction:
- Cohort design: Participants selected by exposure → followed for outcomes 1
- Case-control design: Participants selected by outcome → look back at exposures 6
- Cross-sectional design: Both exposure and outcome measured simultaneously at one point in time 6
- RCT: Investigators randomly assign the exposure 6
Why Other Options Are Incorrect
This cannot be a cross-sectional study (C) because cross-sectional studies measure exposure and outcome at the same single point in time, described as taking a "snapshot" of a population. 6 The question implies following groups over time to compare health outcomes, not simultaneous measurement.
This cannot be a case-control study (B) because participants are not selected based on having or not having a disease outcome and then looking backward at their TV watching habits. 6
This cannot be an RCT (D) because there is no randomization of participants to TV watching groups—individuals self-select their TV watching behavior. 6
Clinical Context
Cohort studies are particularly useful for examining multiple health outcomes following a single exposure (in this case, TV watching habits). 3 They establish temporal relationships between exposure and outcome, which is essential for understanding causality. 5 The longitudinal nature allows calculation of incidence rates and relative risks. 3