University of York Department of Health Sciences Applied Biostatistics
Exercise: Correlation and Regression
Question 1 In a study of blood pressure during pregnancy and foetal growth, 209 healthy women having their first pregnancy had 24 hour blood pressure readings taken in mid-pregnancy. The size of the baby was recorded at birth. The abstract included the following: ‘It was found that a 5 mm Hg increase in mean 24 hour diastolic blood pressure at 28 weeks’ gestation was associated with a 68 g (95% CI 3 - 132) decrease in birth weight . . . Maternal mean 24 hour diastolic blood pressure at 28 weeks’ gestation was also inversely associated with the infant’s ponderal index (weight/height3) at birth . . . (P=0.06).’ (Churchill and Beevers 1996). (N.B.: weight/height3 is the usual ponderal index for infants, rather than weight/height2 as is used for adults and older children.) a) c) What method would be used to calculate the 68g per 5 mm Hg? What is meant by ‘increase’ and..