Is it measured from the middle of the normal range or from one of the edges and if so which edge? And is the point it is measured from adjusted for sex, so that a girl's delay would tend to be 15 months but she might be identical to a boy with a 12 month delay?
Many thanks in advance! It has been really bugging me when I see these references and can't figure out what they might mean!
By the way, quick thank you to Moondog for the recommendation of the author of "Listen to your Child". After I'd gone through it with a pen changing all the references to when things happen (I added another year to make it less painful!), I managed to read it with pleasure. Very helpful to start getting more familiarity with normal development.