Internal Validity (IV)
The level of control for the possible effects of extraneous variables on the dependent variable.
External Validity (EV)
The level of generalizability of the study results to other groups/settings beyond those in the current experiment.
Threats to internal validity
Extraneous factors that affect the dependent variable.
IV/History Effect
When events occur b/w the pretest & posttest that impact the dependent variable (& affect participants).possible solution: establish a control group to compare w/ the experimental group.
IV/Maturation Effect
Changes in dependent variable, possibly resulting from elapsed time and not the independent variable.Possible Solution: establish a control group to compare w/ the experimental group.
IV/Baseline
Pretest measurement to obtain the status/level of variable prior to initiating a study.
IV/Testing effect
Exposure to baseline test helps participants/dependent variable to be “test-wise” (perform better on the next test).
IV/Inaccurate instrumentation
Instruments are inaccurate/not calibrated.Possible solution: Calibrate the instruments; use same instrument for pretest and posttest.
IV/Nonstandardized procedures
Procedures are not standardized.PS: Standardize all procedures!
IV/Incorrect written instrumentation
Instrumentation does not accurately measure study objectives (poorly designed questions).PS:Improve instrument questions/design.
IV/Selection bias
Randomly selected study participants may already have experimental effect.PS: Recruit volunteers, then randomly assign them to groups; pretest groups on measures of dependent variables.
IV/Selection Maturation Effect
Different maturation levels of study groups.PS:Pretest/prescreen group members re: maturity levels.
IV/Selection Maturation Effect
Different maturation levels of study groups.PS:Pretest/prescreen group members re: maturity levels.
IV/Statistical Regression
Extreme high/low scores on participant pretest (extreme or minimal gains predicted).PS: Random sample represents full range of abilities.
IV/Mortality/Attrition
Loss of study participants.PS: Oversampling, incentives (to complete study), compare demographic info of participants at beginning and end of study.
IV/Hawthorne Effect
Participant attitudes (not the independent variable) toward participation in the study (because of being studied/observed) affects their behavior.PS: Provide special treatment to control group w/o independent variable, then compare groups.
IV/Placebo Effect
Participant attitudes/expectations (not the independent variable) affects behavior.PS: Blind/double-blind study, placebo provided to control group, then compare groups.
IV/Diffusion Effect
One group’s treatment contaminates another group’s treatment.PS: Keep treatment/control groups totally separate.
IV/Control Group
Participant group which receives no independent variable (treatment).
IV/Location Effect
Treatment groups are located at separate locations (-possibly to prevent Hawthorne Effect), locations/environments are different enough to affect the dependent variable differently.PS: Same location for all participants, or minimize differences at the different locations.
IV/Implementation Effect/Threat
Individual(s) implementing the treatment/dependent variable introduce inequality/bias into the study (one person implements better than another person).PS: Implementers are equally competent and trained; standardized implementation protocol; all implementers work w/ all groups; one neutral presenter for all groups; neutral observers for group presentations.
EV/Selection Treatment Interaction
Overgeneralizing to groups for whom the study results don’t apply.PS: Present data showing intact treatment group is representative of intended population on one/more variables; random sample of participants from study population.
EV/Setting Treatment Interaction
Duplicating the environmental setting/conditions in other settings, due to the differences b/w settings/participants.
EV/History Treatment Interaction
Generalizing findings to past/future situations.PS: Focus applications to the most effective time period; minimize/eliminate effects of extraneous variables at other time periods.