In a mass screening 1,329 men aged 40-59 years were examined with regard to serum cholesterol and systolic blood pressure, and then followed over a 6-year period for the development of coronary heart disease (CHD). At the beginning of the period all were free from CHD.

  Systolic Blood pressure (mm Hg)
< 147 147-166 ³167
(Serum cholesterol
mg/100 ml)		 # Men#Men with CHD # Men #Men with CHD # Men #Men with CHD
< 220 431 10 93 3 49 7
220 - 259347 1974 649 6
³ 260 18519 57 11 44 11

Consider the following groups:

  1. men with serum cholesterol under 220 mg/100 ml and systolic blood pressure under 147 mm Hg;
  2. men with serum cholesterol 260 mg/100 ml and higher, and systolic blood pressure under 147 mm Hg;
  3. men with serum cholesterol under 220 mg/100 ml and systolic blood pressure 167 mm Hg and higher;
  4. men with serum cholesterol 260 mg/100 ml and higher, and systolic blood pressure 167 mm Hg and higher.

Calculate the relative risk of coronary heart disease in relation to group (a) for group (d).