Question

The following table gives Framingham data relating systolic blood pressure (SBP) to coronary heart disease (CHD) after 18 years among those who were free of the disease at first examination.

SBP (mmHg)    CHD+   CHD-      Total

>165          95        201           296

<165         173       894          1067

Total         268      1095         1363

Calculate RD, RR and their associated 95% confidence intervals. Interpret your results.

Answer 1

Answer :)

	CHD+	CHD-
>165	95 (a)	201 (b)
<165	173 (c)	894 (d)

To calculate RR and RD, first, calculate the outcome rate exposed (Pe), and outcome rate not exposed (Pu).

Outcome rate exposed (Pe) = a/(a+c)

Outcome rate exposed (Pe) = 95/(95+173)

Outcome rate exposed (Pe) = 0.35

Outcome rate not exposed (Pu) = b/(b+d)

Outcome rate not exposed (Pu) = 201/(201+894)

Outcome rate not exposed (Pu) = 0.18

Relative risk (RR) = Pe/Pu

Relative risk (RR) = 0.35/0.18

Relative risk (RR) = 1.94

The 95% confidence intervals of RR = 1.94 x 95%

The 95% confidence intervals of RR= 1.843

Risk difference (RD) = Pe – Pu

Risk difference (RD) = 0.35 – 0.18

Risk difference (RD) = 0.17

The 95% confidence intervals of RD = 0.17 x 95%

The 95% confidence intervals of RD= 0.1615

The 95% confidence intervals of RR suggests that RR is at least 1.843 and at least RD is 0.1615.