Biostatistics & Research · patient case question
Which study design provides the highest level of evidence for a therapeutic question?
Patient case: Reading the evidence
demo: Journal club
chief: The practice is reviewing published evidence before making a purchasing decision and interpreting a set of student examination results.
history: Five dental students scored 64, 56, 48, 66 and 66 on an examination. A trial reports three laser devices, each with a mean difference and a 95 percent confidence interval. A separate paper reports a diagnostic test's performance.
meds: Not applicable.
findings: Laser 1: confidence interval crossing zero into negative values, lowest price. Laser 2, an erbium YAG device: confidence interval entirely above zero, mid price. Laser 3: confidence interval crossing zero, highest price.
Show answer and explanation
Correct answer: C. A randomised controlled trial
- A. A case-control study works backwards from outcome to exposure. It suits rare diseases but is prone to recall and selection bias.
- B. A cohort study follows exposed and unexposed groups forward. It is strong for prognosis and harm but remains observational and vulnerable to confounding.
- C. Correct. Among primary studies the randomised controlled trial sits at the top, because randomisation distributes both known and unknown confounders evenly between arms and permits causal inference. Above it in the hierarchy sit only systematic reviews and meta-analyses of such trials.
- D. A case series describes patients without a comparison group and cannot support causal claims.
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