Threats to internal validity

Question	Answer
Explain "history" as a threat to internal validity	Events in the participant's life/environment, other than the independent variable, that occur during the course of the experiment and may affect outcome.
What is "maturation"?	Changes that occur within participants with the passing of time, regardless of the experimental manipulation. Eg, longitudinal effects, or getting bored during a task.
Testing effects	Changes in what is being measured brought about by reactions to the process of measurement. Eg, reducing negative behaviour due to being observed, improving results due to practice effects, etc.
Instrumentation	Unwanted changes in characteristics of the instrument or procedure. Eg, experimenter attitudes varying, inconsistent coder interpretation.
Regression to the mean	Tendency for extreme scores to move (regress) closer to the mean on a retest - the idea here is that average is average for a reason, so for a group, some of the extreme results almost inevitably will be less extreme when repeated.
Selection	Are the comparison groups actually comparable? Is the selection random, is the group assignment random? Or is there bias?
Attrition	Loss of subjects over the course of an experiment. This is particularly an issue if you lose more from one group than another, or if the loss skews the group in terms of characteristics so that they're no longer comparable.

Resource summary

	Created by Rachel Borthwick over 8 years ago