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            Random Assignment

 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
the experiment.