Confidence interval vs P-value
How to tell Confidence interval and P-value apart when a board question makes them look alike.
CI estimates effect range and precision; p-value quantifies incompatibility with the null under assumptions.
Side by side
Confidence interval gives a range of plausible effect sizes and conveys precision; crossing the null often implies nonsignificance at that alpha.
P-value is the probability of observing data at least this extreme if the null hypothesis were true.
Confidence interval gives a range of plausible effect sizes and conveys precision; crossing the null often implies nonsignificance at that alpha.
P-value is the probability of observing data at least this extreme if the null hypothesis were true.
A 95% confidence interval that excludes the null value corresponds to p < 0.05 for a two-sided test; null is RR/OR = 1 or mean difference = 0.
P-value is the probability of observing results at least this extreme if the null hypothesis is true; p < 0.05 usually aligns with a 95% CI excluding null.
The repair move
Before naming the answer, force the stem through the separator: CI estimates effect range and precision; p-value quantifies incompatibility with the null under assumptions.
Try a free question
CoreA randomized trial of a new antihypertensive drug reports that the systolic blood pressure reduction with the drug is 10 mmHg (95% confidence interval 4 to 16 mmHg). What does this confidence interval mean?
Show answer and explanation
Answer: A. The true mean reduction plausibly lies between 4 and 16 mmHg. 95% confidence interval: the range that, under repeated sampling, would capture the true population parameter 95% of the time. For mean differences, null = 0 (no difference); for relative measures like RR/OR, null = 1 (no difference). If the CI EXCLUDES the null value, the result is statistically significant at the corresponding alpha (here p<0.05). CI provides estimate AND precision; p-value provides only a binary significance threshold.
Why the other choices are tempting
- B. P could be much lower than 0.05; CI excluding null only tells us p<0.05.
- C. The CI is the range of plausible true effects, not the range of individual responses.
- D. 95% of patients having reductions in this range describes individual variability, not the CI for the mean.
- E. If CI excludes null, the drug is effective.
Flashcards
Tap a card to flip it.
What clue supports Confidence interval?
Choose Confidence interval when the stem gives this pattern: Confidence interval gives a range of plausible effect sizes and conveys precision; crossing the null often implies nonsignificance at that alpha.
What clue supports P-value?
Choose P-value when the stem gives this contrasting pattern: P-value is the probability of observing data at least this extreme if the null hypothesis were true.
Quick answers
What is the fastest way to tell Confidence interval from P-value?
CI estimates effect range and precision; p-value quantifies incompatibility with the null under assumptions.
What is the key clue for Confidence interval?
Confidence interval gives a range of plausible effect sizes and conveys precision; crossing the null often implies nonsignificance at that alpha.
What is the key clue for P-value?
P-value is the probability of observing data at least this extreme if the null hypothesis were true.