Suggested answer to exercise: Estimation, standard error and confidence intervals, 6

Question 6: What do the confidence intervals for the change in bone mineral content mean? To what population do they refer?

Suggested answer

The two confidence intervals give us a range of values within which the mean change is estimated to lie in the whole population of women who would volunteer if they were to receive the treatment for that group. The confidence interval for the calcium only group tells us that the mean percentage change is a reduction in bone mineral content somewhere between 0.6 and 4.6 percentage points. For the calcium plus exercise group taking the mean percentage change could be a reduction of 0.8 percentage points or an increase of 3.1 percentage points or any value between these limits. These women were volunteers and it is therefore difficult to extrapolate the findings to a general population.

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Last updated: 27 July, 2009.

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