Statistics examplesExample 1: A drug lowered diastolic BP by a mean of 8mmHg from 100 to 92mmHg (p= 0.02; 95% CI = 214mmHg)
Example 2: Comparing two groups (from  Hyperstat ) When you see a confidence interval in a published medical report, you should look for two things. First does the interval contain a value that implies no change or no effect ? For example, with a confidence interval for a difference look to see whether that interval includes zero. With a confidence interval for a ratio, look to see whether that interval contains one. Here's an example of a confidence interval that contains the null value. The interval shown below implies no statistically significant change .
Here's an example of a confidence interval that excludes the null value. If we assume that larger implies better, then the interval shown below would imply a statistically significant improvement .
Here's a different example of a confidence interval that excludes the null value. The interval shown below implies a statistically significant decline .
Practical significance You should also see whether the confidence interval lies partly or entirely within a range of clinical indifference . Clinical indifference represents values of such a trivial size that you would not want to change your current practice. For example, you would not recommend a special diet that showed a one year weight loss of only five pounds. You would not order a diagnostic test that had a predictive value of less than 50%. Clinical indifference is a medical judgement, and not a statistical judgement . It depends on your knowledge of the range of possible treatments, their costs, and their side effects. As statistician, I can only speculate on what a range of clinical indifference is. I do want to emphasize, however, that if a confidence interval is contained entirely within your range of clinical indifference , then you have clear and convincing evidence to keep doing things the same way (see below).
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