The Threat Of A Pre Post Design Essay
History threat- This occurs when the study outcome is affected by some historical event. If a specific event or chain of events does transpire during the time when a treatment is administered and it affects the observations it is a threat to the internal validity. Often times there is no way of determining if the historical event(s) or the treatment accounts for the results found.
Maturation threat- Between pre- and postmeasurement, this is a threat to validity resulting from normal development changes in participants between the pretext and the post test that could affect the results. Maturation threat differs from history threat in that it isn’t specific in which event or chain of events could cause the outcome but instead consist of all the events that naturally occur in one’s life that could cause the outcome.
Testing threat- Using a pre-post design, if taking the pretest affects how participants do on the posttest, a threat to internal validity is said to occur. For this reason, effects of testing should always be considered when pretests are given.
Instrumentation threat- This arises when, in a pretest-posttest situation, a change in observers, measuring device, or procedure used on the pretest and posttest differ.
Mortality/Attrition threat- When a significant number of participants drop out which has the potential of biasing results.…