[mlthoughts2018]

The criticism that it would go negative in the past is meaningless. Of course it’s unphysical, but that doesn’t mean a linear model isn’t appropriate for today’s data.

You would just choose a point of time in the past where you believe the model is inapplicable. Maybe it was a different linear model then, or maybe mostly constant, who cares, we’re modeling today’s range of data, which might be well explained by a linear model, doesn’t really matter what 2011’s data was doing unless we separately believe the same growth law had to apply across all the years, and I see no reason why.