Suggested answer to exercise: Education for atopic dermatitis, 2

The main outcome measure was severity of eczema as a score on an atopic dermatitis scale. The abstract contained the following:

‘Significant improvements in severity of eczema and subjective severity were seen in all intervention groups compared with control groups (total score for severity: age 3 months to 7 years –17.5, 95% confidence intervals –19.6 to –15.3 v –12.2, –14.3 to –10.1 . . .)’ These numbers are the mean change in severity score, before minus after, over 12 months.

Question 2: What would be a better confidence interval than those presented?

Suggested answer:

A better confidence interval would be for the difference between the two mean changes.

This is actually given in Table 3 of the paper. The point estimate of the difference is –5.2 with 95% confidence interval –8.2 to –2.2 scale points. This shows that the effect of the education is estimated to be to reduce average severity score by between 2 and 8 points, compared to no education.

This is much less than the natural reduction over time, but is in addition to it.

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