Keith

If you divide the graph in two you see that up until a few years ago, the graph was pretty much horizontal for at least a decade.

Then in about 2003 or thereabouts it changed direction and started climbing.

Since it changed direction, it can be said that the new direction has been pretty linear so far.

However, if you look at the graph as a whole you see that it is a dog leg, with a significant change of direction happening that has caused the 500% increase.

The whole graph in its entirety going back over the last couple of decades is NOT linear.

You are a physicist and you will therefore be aware that the more variables there are in a given situation, the more unlikely it is that smooth graphs will be derived from observations of reality.

There are so many factors to consider in this issue that we can only comment on general trends.

In this case, the general trend was flat, and then it changed recently to one of sustained growth.

What does that change signify, why did it happen and can it happen again?

If we had made predictions in 2003 about what was going to happen next based on what had happened before, we would have said that hetero infection would carry on on a horizontal trajectory.

We would have been wrong.

It follows that we can't predict a consitent linearity to the growth in hetero infections based on a limited sample from 2003 onwards.

We have to acknowledge that if the graph has radically changed in nature before, then iit could do it again.

The whole graph has not been linear, and we cannot say with any confidence whether there wiill be an epidemic in 140 years or 14.