If you take the population and divide by the rate of housing starts per year, you get a quantity in dimensions of time and units of years. This quantity roughly speaking is related to the "longevity of a dwelling" you need to have in order for the housing per person that's available not to decline. So if real longevity of houses is more or less a constant, then when this graph is high housing availability is declining, and when it's low it's growing... There's a reason millennials feel cheated
