In which type of sampling do researchers identify a small number of individuals who possess the target characteristics, and then use them as informants to identify and locate others who qualify for inclusion in the study?

Given below are two statements: one is labeled as Assertion (A) and the other is labeled as Reason (R). Assertion (A): Though ex-post facto research examines cause and effect relationships, it is not part of experimental research. Reason (R): In ex-post facto research, the effect or change in the independent variable has already occurred and cannot be manipulated. In the light of the above statements, choose the most appropriate answer from the options given below:

Given below are two statements: one is labeled as Assertion (A) and the other is labeled as Reason (R). Assertion (A): In non-probability sampling, the units are selected at the discretion of the researcher. Reason (R): Non-probability samples do not require a sampling frame. In the light of the above statements, choose the most appropriate answer from the options given below: