Final answer:
Direct vs. Indirect is a classification in observable studies, where characteristics are measured in a sample without manipulating variables. The results depend on the size and randomness of the sample.
Step-by-step explanation:
The classification of Direct vs. Indirect is a method of observation in observational studies. In an observational study, characteristics are measured in a sample without manipulating variables of interest. For example, a political poll that measures the opinions of potential voters is an observational study. The results of an observational study depend on the size and randomness of the sample and provide a snapshot in time of the population's characteristics.