Answer
a) Stratified random sampling
b) Simple random sampling
c) Convenience sampling
Work Step by Step
a) Stratified random sampling. To have been chosen at random, 200 male and 200 female, the population must have been divided into two strata: Male and Female. Stratified random sampling is necessary if the population contains homogeneous groups. The potential source of bias here is overlapping. This happens in case a person is does not conform to traditional genders.
b) Simple random sampling. Out of all the customers, 625 of them are selected. The population, in this case, is all the customers of that store. Intentional bias might occur if the interviewer selects his favorite customers.
c ) Convenience sampling. The teachers were questioned at the researcher's convenience. This technique might provide bias because it is possible to question a teacher more than once.
