Random Sampling vs. Random Assignment
Random sampling and random assignment are fundamental concepts in the realm of research methods and statistics. However, many students struggle to differentiate between these two concepts, and very often use these terms interchangeably. Here we will explain the distinction between random sampling and random assignment.
Random sampling refers to the method you use to select individuals from the population to participate in your study. In other words, random sampling means that you are randomly selecting individuals from the population to participate in your study. This sampling helps ensure the sample’s representativeness, supporting external validity. A sample is truly random only if the researcher selects every individual in the population with equal probability for the study. In practice, researchers rarely use “true” random sampling because ensuring that every individual in the population has an equal chance of selection, that is often not feasible. For this reason, it is especially important to avoid using the term “random sample” if your study uses a nonprobability sampling method (such as convenience sampling).
Random assignment refers to the method you use to place participants into groups in an experimental study. For example, say you are conducting a study comparing the blood pressure of patients after taking aspirin or a placebo. You compare patients taking aspirin (experimental) and a placebo (control). Ideally, you randomly assign participants to either the experimental or control group, giving each an equal chance.
This eliminates systematic differences between the groups before administering the treatment (e.g., aspirin or placebo). Random assignment ensures group differences stem from the treatment, not confounding variables.
So, to summarize, random sampling refers to how you select individuals from the population to participate in your study. Random assignment refers to how you place those participants into groups (such as experimental vs. control). Knowing this distinction will help you clearly and accurately describe the methods you use to collect your data and conduct your study.
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