Keith,

I wasn't looking for an explanation, I was simply pointing out that the graph, taken over a 20-30 year peiod, is not linear.

The anomaly in the original line turned out not to be a flash in the pan, but a sustained change of circumstances.

On that basis, we cannot make a claim, based on past experience, that the growth rates among hetero's will continue to grow in a consistently linear fashion.

It may happen that way, but it could also be the case, based on past form, that as overall numbers increase, that growth rates also increase.