Is smoking during pregnancy associated with more premature births?
To investigate this question, researchers decide to examine pregnancy length (this is the variable.) They select a random sample of 114 pregnant women who were smokers. The average pregnancy length for this sample of smokers was 260 days.
From a large body of research, it is known that length of human pregnancy has a standard deviation of 16 days. The researchers assume that smoking does not affect the variability in pregnancy length.