Gaffney et al (1994) compared 141 babies who developed cerebral palsy to a control group of (control) babies made up from the babies who appeared immediately after each cerebral palsy case in the hospital delivery book. The corresponding hospital notes were reviewed by a researcher, who was blind to the baby’s outcome, with respect to medical staff response to signs of fetal stress. Failure to respond to signs of fetal distress by the medical staff was noted in 25.8% of the cerebral palsy babies and in 7.1%

of the next delivery controls: a difference of 18.7%. This difference had standard error 4.2% and the 95% CI was 10.5 to 26.9%.

(a) What is the statistical null hypothesis for this study? What is the alternative hypothesis?

(b) What is meant by ‘the difference was 18.7%’?

(c) What can we conclude from the 95% CI?