submariners spend months under 100% artificial light, do they have a higher incidence of pd? what about those living in the far north with months of darkness and also under 100% artificial light?
wonder what inspired these researchers to open this can of worms.

i have always assumed pd distribution in the u.s is somewhat removed from the causitive factors since numbers often taken from medicare statistics and as people age they often move to the city and/or warmer climates.