An important procedure in conducting research is random
assignment. What is random assignment? Below is a definition
of random assignment:
Random Assignment Definition
Random assignment is a procedure in conducting experiments
in which each participant has the same probability of being
assigned to a particular condition of the experiment.
Random Assignment Example
Imagine that a researcher was interested in the influence of
music on job motivation. Some participants would be assigned
to a condition in which they would hear music while working.
Other participants would be assigned to a condition in which
they would not hear music while working. A coin could be
flipped to determine which condition each participant is
assigned to. This would reflect a random process.
The Importance of Random Assignment
Why would a researcher randomly assign participants to
conditions? Random assignment can allow researchers to make
causal conclusions about the effect of one variable on another
variable. Random assignment allows the researchers to rule out
explanations based on personality and individual difference
variables. Random assignment makes it equally likely that a
participant with a certain characteristic is in each condition of
Random assignment of participants to experimental conditions is a commonly used experimental technique to help ensure that the treatment group and the control group are the same before treatment. For example, let us assume that we're curious to know the effects of eating an apple a day on your health (measured by blood pressure). One way of designing the study would be to select a sample of people and divide them into a control group (i.e., those who don't have an apple a day) and a treatment group (i.e., those who do have an apple a day). How do you decide to divide your subjects? The best way is to do it randomly in order to cancel out the idiosyncrasies of your subject pool. Imagine if you decided to choose the groups based on cholesterol intake. You decide to have the low cholesterol group in the control group and the high cholesterol group in the treatment group. Would this bias the results of your study? Yes. Since cholesterol affects blood pressure, you as an experimenter would not know if the changes in health were due to the apple a day or the amount of cholesterol intake.
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