Biostatistics & Research · patient case question
Based on the confidence intervals reported, which laser should the practice purchase?
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. Laser 2, the erbium YAG, whose interval lies entirely above zero
- A. Price is not evidence. Laser 3 is both the most expensive and unproven.
- B. Point estimates alone do not establish significance. Two devices can share an estimate and reach opposite conclusions depending on the width of their intervals, which is the entire lesson of this item.
- C. Correct. Only Laser 2 has an interval that excludes zero, so it is the only device with a statistically significant benefit. An interval crossing zero means the true effect could plausibly be nil or harmful. Price is a consideration only among options that actually work.
- D. A cheaper device with an interval crossing zero has not been shown to work. Buying it saves money on an ineffective purchase.
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