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Suppose you read the following statement:

The mean value for the intervention group was 29 points lower than for the control group (p-value < 0.05). This might correspond to either of the following 95% confidence intervals:

- Treatment difference: 29.3 (22.4, 36.2)
- Treatment difference: 29.3 (11.8, 46.8)

If exact p-value is reported, then the relationship between confidence intervals and hypothesis testing is very close. However, the objective of the two methods is different:

- Hypothesis testing relates to a single conclusion of statistical significance vs. no statistical significance.
- Confidence intervals provide a range of plausible values for your population.

- Use hypothesis testing when you want to do a strict comparison with a pre-specified hypothesis and significance level.
- Use confidence intervals to describe the magnitude of an effect (e.g., mean difference, odds ratio, etc.) or when you want to describe a single sample.

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rev. 05-Aug-2019