We know how difficult it is to find a convincing instrumental variable Zi to overcome the "unobserved ability" problem in a wage regression to...

We know how difficult it is to find a convincing instrumental variable Zi to overcome the "unobserved ability" problem in a wage regression to measure the returns to education. Critically discuss whether ="distance in miles of high school location of worker to closest four year college"satisfies the two properties of a valid instrument. [This instrument was suggested in Card, D. (1995) Using geographic variation in college proximity to estimate the return to schooling. In L.N. Christofides, E.K. Grant, & R. Swidinsky (eds.),Aspects of LaborMarket Behaviour: Essays in Honour of John Vanderkamp. University of Toronto Press.]

How about

Zi ="family wealth of workeri when 18 years of age"?