> Because there is a fairly strong correlation with unemployment and cognitive indicators
You're arguing that there's an endogeneity effect -- that poor cognition causes less working? That's a common problem. The authors discuss their use of an instrumental variable technique to avoid this issue.
> parabola is already being "forced down" near hours worked = 0
Not sure what you mean. Typically a model like this includes a constant to allow for a non-zero dependent variable when all the explanatory variables are zero. To do otherwise in this case would be absurd. The idea that the average non-working person has zero cognitive function...
That's exactly what I'm asking for: a clearer explanation.
I don't believe the paper's conclusion, but I don't understand your criticism of it. If you're saying the estimated curve is inappropriate, a better argument would be that they should include more terms of the work-hours Taylor expansion to get a better fit. Or perhaps there are confounding variables left out of the model.
You're arguing that there's an endogeneity effect -- that poor cognition causes less working? That's a common problem. The authors discuss their use of an instrumental variable technique to avoid this issue.
> parabola is already being "forced down" near hours worked = 0
Not sure what you mean. Typically a model like this includes a constant to allow for a non-zero dependent variable when all the explanatory variables are zero. To do otherwise in this case would be absurd. The idea that the average non-working person has zero cognitive function...
> smooth, quadratic curve, is a mirage
Ever heard of a Taylor polynomial?