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Exercise: Diabetes and high blood pressure in the 2005 M.Sc. questionnaire, Part 2, 1

Question 1: The program used for the analysis in Week 7 (Stata 8) gives the following statistics:

Risk difference = 0.196 (95% CI -0.091 to 0.483)

Risk ratio = 2.88 (95% CI 1.02 to 8.10)

Odds ratio = 3.69 (95% CI 0.96 to 14.32)

What do each of these statistics mean?

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Suggested answer

Risk difference = the difference between the proportion of diabetics
who report high blood pressure and the proportion of non-diabetics who report high blood pressure,
3/10 - 20/192 = 0.3000 - 0.1042 = 0.196.

Risk ratio = the proportion of diabetics who report high blood pressure
divided by the proportion of non-diabetics who report high blood pressure,
(3/10) / (20/192) = 0.3000 / 0.1042 = 2.88.

The odds of high blood pressure is the number with high blood pressure divided by
the number without high blood pressure.

Odds ratio = the odds of reporting high blood pressure among diabetics
divided by the odds of reporting high blood pressure among non-diabetics,
(3/7) / (20/172) = 0.4286 / 0.1163 = 3.69.

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Last updated: 20 November, 2006.

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