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When researchers need to select a representative sample from a larger population, they often utilize a method known as random selection. In this selection process, each member of a group stands an equal chance of being chosen as a participant in the study.
Random Selection vs. Random Assignment
How does random selection differ fromrandom assignment? Random selection refers tohow the sample is drawnfrom the population as a whole, whereas random assignment refers tohow the participants are then assignedto either the experimental or control groups.
It is possible to have both random selection and random assignment in an experiment.
Imagine that you use random selection to draw 500 people from a population to participate in your study. You then use random assignment to assign 250 of your participants to acontrol group(the group that does not receive the treatment or independent variable) and you assign 250 of the participants to the experimental group (the group that receives the treatment or independent variable).
Why do researchers utilize random selection? The purpose is to increase the generalizability of the results.
By drawing a random sample from a larger population, the goal is that the sample will be representative of the larger group and less likely to be subject to bias.
Factors Involved
Imagine a researcher is selecting people to participate in a study. To pick participants, they may choose people using a technique that is the statistical equivalent of a coin toss.
Another important thing to remember is that larger sample sizes tend to be more representative. Even random selection can lead to a biased or limited sample if the sample size is small.
When the sample size is small, an unusual participant can have an undue influence over the sample as a whole. Using a larger sample size tends to dilute the effects of unusual participants and prevent them from skewing the results.
The Experimental Group In Psychology Experiments
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Elmes DG, Kantowitz BH, Roediger HL.Research Methods in Psychology.Belmont, CA: Wadsworth; 2012.
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