## RCT vs Cohort Study: Key Distinguishing Feature ### Core Difference: Allocation of Intervention **Key Point:** The fundamental distinction between an RCT and a cohort study is that in an RCT, the investigator ACTIVELY ASSIGNS the intervention using a random process, whereas in a cohort study, the investigator merely OBSERVES naturally occurring exposure groups. ### Comparison Table | Feature | RCT | Cohort Study | |---------|-----|---------------| | **Intervention assignment** | Investigator assigns randomly | Participants self-select or naturally exposed | | **Control of confounding** | Randomization balances confounders | Matching, stratification, or statistical adjustment needed | | **Causality inference** | Gold standard (can establish cause–effect) | Association only (cannot definitively prove causation) | | **Bias risk** | Lower (if properly conducted) | Higher (selection bias, confounding) | | **Feasibility** | Limited (ethical, practical constraints) | Broader applicability | | **Cost & time** | Higher | Lower | ### Why Active Random Assignment Matters **High-Yield:** Random assignment by the investigator is what eliminates selection bias and balances unknown confounders — this is the defining methodological feature that elevates RCTs above all other observational designs [cite:Park 26e Ch 10]. **Mnemonic:** **RACED** — RCT = **R**andom **A**ssignment by investigator; **C**ohort = **C**hoice/natural exposure; **E**xperimental vs observational; **D**ifferent causal inference strength. ### Why Other Options Are Incorrect - Sample size and duration are not defining features — an RCT can be small or short; a cohort study can be large or long. - Blinding is a quality enhancement but not the distinguishing feature — both RCTs and cohort studies can use blinded outcome assessment.
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