Chapter three: the study of adult development and aging: research methods. Studies of aging use the quasi-experimental design (p. 45) Term used to describe the process of comparing groups on predetermined characteristics. Longitudinal designs (p. 47) people are followed repeatedly over time. Sequential research designs (p. 53) longitudinal plus cross-sectional designs. The most efficient design a set of three designs manipulating the variables of age, cohort and time of measurement time-sequential design (age by time of measurement) cohort-sequential design (cohort by age) cross-sequential design (cohort by time of measurement) Correlational designs(p. 55) relationships are observed among variables as they exist in the world. Simple correlational designs (p. 55) two variables are related, but a researcher cannot know which came first possibility that a third unknown variable accounts for the apparent relationship between the two observed variables. Laboratory studies participants are tested in a systematic function using standardized procedures.