Differences in clients. The characteristics of the client—age, sex, ethnicity, socio-economic status, and so on—can affect the extent to which results can be generalized. Since clients in...

Differences in clients. The characteristics of the client—age, sex, ethnicity, socio-economic status, and so on—can affect the extent to which results can be generalized. Since clients in single-system designs are almost never randomly selected from a population, one can never be sure the clients in a single-system design are representative of any other group. Example: Nick devised a counseling program that was very successful in decreasing dropouts in one school with mainly middleclass students. But when Nick tried to implement his program in a different school, one with largely low-income students, he found the dropout rate was hardly affected.