Biostatistics & Research · patient case question
What is preferable about a confidence interval?
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: A. A narrower interval, which indicates greater precision
- A. Correct. A narrow interval means the estimate is precise and the true value is pinned within a tight range. Width is driven mainly by sample size, so narrow intervals generally reflect larger, better-powered studies.
- B. A wide interval reflects uncertainty and imprecision. It is less useful, not more.
- C. An interval that includes the null, meaning zero for a difference or one for a ratio, indicates the result is not statistically significant.
- D. The 95 percent interval is the biomedical standard. A 90 percent interval is narrower only because it is less conservative, which is not a real gain in precision.
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