2 evaluation criteria: internal and external validity
*Definition: Internal validity asks if it's the independent variable (IV) (or something else) that caused or resulted in the change in the dependent variable.
*It refers to INSIDE of the study.
*To establish internal validity the researcher rules out other variables that threaten the relationship between the IV and DV. These factors or threats are:
In depth explanation to threats of internal validity:
- Selection bias
: events that occur over time or the course of a study.
a lack of randomization with sampling.
•Maturation: events that occur within participants over the study's time.
- •Diffusion: one subject from one group talks to a subject from
- another group.
- Both groups end up being affected by the treatment.
: taking the same test more than once such as in a pre-test & post-test.
: a loss of subject between points of data collection (drop out).
: faulty equipment or a lack of consistency in observation or data collection.
Definition: Questions the conditions under which the findings can be generalized (generalizability).
Deals with the ability to generalize the findings outside the study to the larger population & to other contexts.
Threats to external validity:
- •Selection of subjects.
- •Reactive effects or study conditions.
- •Measurement or testing effects.
: Who is being studied. Has a representative sample been obtained of the larger population. How has the sample been obtained. Is the sample size large enough?
: a participant’s reaction to being studied. The Hawthorne Effect
where the participant reacts in a certain way not to the IV but because they are in a study.
: A pre-test administered affects the post-test results & does affect the ability to generalize the study findings to other populations. The pre-test primes the participants.
All in all....