A linear regression would be theoretically wonky, since the Y-axis is upper bounded at 100%. So, by the time the graph hits values like 80%, it should start to

A linear regression would be theoretically wonky, since the Y-axis is upper bounded at 100%. So, by the time the graph hits values like 80%, it should start to get "saturated" and flatten out. This fit, with A approximately 100 does a good job of that. Clearly, the fit is bad near the origin (for small purchasing power), so maybe one can expect a modification at small values of x; I'm not sure if that that will correspond to small values of y.