Surveillance of congenital rubella in Great Britain

Children born after intracytoplasmic sperm injection What do authors mean by control infants?Editor-Sutcliffe et al compare babies born through intracytoplasmic sperm injection with control babies (matched for social class, maternal education, region, and sex) born after unassisted conception. 1 In their table they give means, standard deviations, and 95% confidence intervals for the two groups separately.These confidence intervals tell us about the estimation of the mean in the population of which the babies are a random sample, which they are not.They tell us nothing about the comparison between the cases and controls.These controls have been chosen to be similar to the study babies in many ways; they are not a representative sample of babies.It is the difference between the study babies and the control babies that is of interest, and the confidence interval we should have is that for this difference in mean.We cannot work this out from the data given, because this is a paired study and we have unpaired standard deviations.All we have for the comparison is the implication, not actually stated, that the differences are not significant.What we should be given are confidence intervals that tell us how different the cases and controls are.