Psyc 357 ch 3: the study of adult development and aging: research methods: variables in developmental research, variable=characteristics that varies from indiv to indiv. Dependent variable= variable on which ppl differ. Independent variable=variable that explains/causes range of scores in the. Dv: tx age as iv but it"s not technically something you can manipulate, experimental design= manipulation of an iv followed by the measurement of scores on the dv. Ppl randomly assigned to tx and ctrl groups: quasi-experimental design= groups compared on predetermined characteristics. Can"t conclude that predetermined characteristics caused variations in. Dv but can describe difs b/w groups: descriptive research designs, major challenge is to separate effect of aging from effects of time. Time of measurement= year or period when testing happens, convenient way of representing social and historical influences on person. Linked to cohort in taht ppl of certain age being tested at particular time must be from same cohort.