2-15 Confidence intervals should be reported

The observed difference in outcomes is the best estimate of how effective or safe treatments are (or would be, if the comparison were made in many more people). However, because of the play of chance, the true difference may be larger or smaller. The confidence interval is the range within which the true difference is likely to lie, after taking into account the play of chance. Although a confidence interval (margin of error) is more informative than a p-value, the latter is often reported. P-values are often misinterpreted to mean that treatments have or do not have important effects.

Understanding a confidence interval may be necessary to understand the reliability of an estimated treatment effect. Whenever possible, consider confidence intervals when assessing estimates of treatment effects. Do not be misled by p-values.

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Confidence Intervals – CASP

The p-value gives no direct indication of how large or important the estimated effect size is. So, confidence intervals are often preferred.

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Know Your Chances

This book has been shown in two randomized trials to improve peoples' understanding of risk in the context of health care choices.

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P Values – CASP

Statistical significance is usually assessed by appeal to a p-value, a probability, which can take any value between 0 and 1 (certain).


False Precision

The use of p-values to indicate the probability of something occurring by chance may be misleading.


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