Assignment 2: Methodology - PTSD

Factors Jeopardizing Internal Validity When designing the data collection strategy for a research study, the researcher must consider issues related to internal validity in order to control the identified threats through the design strategy. Take some time to explore these different threats as you will need to consider these when you perform your own research.

• History The specific events that occur between the first and second measurements.

• Maturation The processes within subjects that act as a function of the passage of time, that is, if the project lasts a few years, most participants may improve their performance regardless of the treatment.

• Testing The effects of taking a test on the outcomes of taking a second test.

• Instrumentation The changes in the instrument, observers, or scorers that may produce changes in outcomes.

• Statistical Regression Also known as regression to the mean. This threat is caused by the selection of subjects on the basis of extreme scores or characteristics. “Give me forty of your worst students, and I guarantee that they will show immediate improvement right after my treatment.”

Provided below are the additional threats that you will need to consider when you perform your own program evaluation.

• Selection of Subjects Some of the biases that may result in the selection of comparison groups are:

o Convenience/availability

o Volunteers versus nonvolunteers

o Early versus latecomers

• Experimental Mortality Experimental mortality means the loss of subjects. For example, a web-based instruction project entitled “Eruditio” was started with 161 subjects but only 95 completed the entire module. Those who stayed in the project all the way to the end may be more motivated to learn and, thus, achieved higher performance.

Page 1 of 2 Research and Evaluation Design

© 2013 Argosy University

2

Factors Jeopardizing Internal Validity

• Selection–Maturation Interaction The selection of comparison groups and maturation interacting, which may lead to confounding outcomes and erroneous interpretation that the treatment caused the effect.

• The Hawthorne Effect The knowledge that one is being observed or that a new program is being offered may positively affect people’s behavior in and of itself.

Page 2 of 2 Research and Evaluation Design

© 2013 Argosy University