Regression to the mean is the procedure first noted by Sir Francis Galton that 'each peculiarity in man is shared by his kinsmen, but on average to the less degree.' Hence the tendency, for instance, for tall parents to produce tall offspring but then who, on average, is shorter than their own parents. The term is now usually used to label the phenomenon that a variable which is extreme on its first measurement will tend to be closer to the centre of the distribution for the later measurement. For instance, in a screening programme for hypertension, only the persons with high blood pressure are asked to return for the second measure. On an average, the second measure taken will be less than the first measure.