A door-to-door survey by Edinburgh's education department of 3,500 new properties, backed by information from the builder Wimpey on 2,000 new homes, provides the procreative information planners have yearned for.
Evidence shows some correlation with what goes on behind closed doors and room size and number. Flatted units generate as few as seven children of all ages per 100 houses.
Planners are now likely to back infill sites with small flatted developments since they now know it will not lead to a plethora of pregnancies, a wad of weans or a batch of bairns.
But beware of Brookies. Three-bedroomed units or above, whether terraced, semi-detached or detached, could generate between 50 and 100 children of all ages per 100 houses. Families migrate towards them. But secondary schools can relax. It takes years before they filter through the system.
The good or bad news, depending on the planners' view, is that housing associations produce most children. Edinburgh officials say association allocation policies link the size of the house to family size.