The confidence interval is also informative in cases where you don’t get a statistically significant result—that is, where the confidence interval contains zero. If the confidence interval is [−0.5%, 0.5%], then the reason you didn’t get statistical significance is because you have good evidence the intervention doesn’t do anything. If the confidence interval is [−20%, 20%], the reason you didn’t get statistical significance is because you have no idea whether the intervention has an effect, or in which direction it goes. Those two outcomes look the same from the viewpoint of statistical
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