Participants enter a research study with unique charac- teristics that produce different scores from one person to another. for an independent-measures study, these individual differences can cause problems. identify the problems and briefly explain how they are eliminated or reduced with a repeated-measures study.

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.