Researchers at one point in time assess and compare the performance of different age groups on the sat. the procedure used in this research best illustrates:

cross-sectional

Explanation:

cross-sectional study is a kind of study which investigate variables through analyzed the data collected in one specific time for a population.  In this study, sample of participants are the same in all variables except one.

in the mentioned research, changing variable is age.

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.