Biostatistics & Research · patient case question
Which statistic expresses the probability that a result occurred by chance alone?
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. The p value
- A. A confidence interval gives a range of plausible values for the true effect and conveys both direction and precision, which is more information than a p value, but it is not itself a probability of chance.
- B. Effect size expresses the magnitude of a difference and is what determines clinical relevance.
- C. Correct. The p value is the probability of obtaining a result at least as extreme as the one observed, assuming the null hypothesis is true. Conventionally a value below 0.05 is called statistically significant. It says nothing about the size of the effect or its clinical importance.
- D. Specificity is a property of a diagnostic test, not a measure of statistical significance.
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