K. warner schaie developed the first study of adult intelligence.

K. warner Schaie developed the first longitudinal study of adult intelligence.

He is a psychologist and a gerontologist who developed the Seattle longitudinal study (SLS) in 1956. The study focuses on understanding cognition and ageing and it was conducted by testing the mental and physical abilities of the subject study.

Some of the findings from his study are listed below:

for many centuries there were important factors which the economies of the muslim empires developed increasingly. they applied economic procedures in production, investment, finance, taxation and property. they used to tax certain goods (for example: harvest), they charged interest on money lent, they signed contracts with merchants; they relied on a common currency, and they used checks as well as promissory notes. with the money collected by means of taxation, the government provided the needy with an income. in addition, trading networks covered huge distances, so far regions started to have contact and exchange goods. this trade network covered areas of asia, africa and europe.