This tutorial is a component of the courseware of the
Centre for Social Sciences - Psychology
Athabasca University. It was authored by Dr.
David Polson, Adjunct Assistant Professor at the University of
Victoria. Dr. Cheuk Ng, Dr. Lyle Grant and Dean Mah of Athabasca
University provided various content-related, technical and
instructional-design assistance. Some
technical notes provide some information about the
instructional-design principles on which the tutorial is based.
In Part 1 of this tutorial, you will be introduced to nine sources
of threat to internal validity.
Campbell & Stanley, 1963)
First, some relevant terms are defined. Then, some background
explanation for a hypothetical experiment is presented. Finally, each
of the nine threats is described, followed by an example and a
contrasting nonexample as applied to the hypothetical experiment. An
explanation is included of why the example represents a threat to
internal validity and why the nonexample is not a threat.
In Part 2 of this tutorial, you will be asked to classify 36
hypothetical experiments as internally valid or not. If not, you must
select the threat to internal validity from one of the nine sources
introduced in Part 1.
Following some of the vignettes in this tutorial, a reference is
made to a "Related Source." This reference is included for students
interested in pursuing the subject matter of the vignette. Sometimes
the details of the hypothetical experiment are very similar to the
related source, but in many cases they are quite different. Thus, the
hypothetical experiment is not to be regarded as an accurate
description of the related source -- the commonality between the two
may simply be similar independent and dependent variables.