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External and Internal Validity
Module 7B
20
Other
Graduate
11/07/2014

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Term
Internal Validity
Definition
  • Occurs when an observed effect of an independent variable on a dependent variable is not caused by extraneous factors.
  • If there are alternate explanations for effect on independent variable, internal validity is threatened.
Term
External Validity
Definition
  • The ability to generalize study results to other groups and settings beyond those in current study.
  • Research that can be generalized will have more practical value and applications for the researcher.
Term
Control Group
Definition
  • A group of participants exactly like the treatment group with the exception that the control group receives no treatment.
  • Valuable for researcher to compare results of treatment group against. 
Term
Experimental Group
Definition
  • The group that receives the experiement or treatment.
  • Compared to control group to examine effects of testing.
Term
Baseline
Definition
  • Measurement taken to establish status or level of variable before any experimentation begins.
  • Used to measure the effectiveness of a test or program.
  • Problems arise when participants learn to test better, effecting the internal validity.
  • Differences between pre and post test can be attributed to testing effects and not results from the actual testing.
Term
History Effect
Definition
  • Threatens internal validity when outside events occur between pre and post testing.
  • Impossible for researcher to control all elements of stress, natural disaster, current events, illness, etc.
  • Depeneding on how study was designed, may be impossible to determine what caused recorded effects.
Term
Maturation Effect
Definition
  • When changes are observed in subject due to elapsed time since study began and may not be the result of any study or testing.
  • A control group might eliminate the threat of maturation to internal validity.
Term
Instrumentation
Definition
  • What a reasearcher uses to collect data.
  • There are different instrumentation designs for various kinds of data and research. Well deigned instruments should reduce threat to internal validity.
  • Instruments may not be accurate or precise enough to measure what researcher wants to measure.
Term
Selection Bias
Definition
  • Occurs any time participants are selected for a study using a non-randomized model.
  • When selection bias is present, it will reduce internal validity.
Term
Selection Maturation Effect
Definition
  • Occurs when using an intact group that varies in their maturation level.
  • Combines weaknesses of maturation and selection bias.
  • Prescreening groups on maturity levels may lessen threat to internal validity.
Term
Statistical Regression
Definition
  • Occurs when particpants are selected based on exteremly high or extremely low test scores.
  • As high testers woud have no where to go but down, and low testers no where but up, internal validity is threatened.
  • Randomizing would counter the threat to internal validity.
Term
Mortality/Attrition
Definition
  • Losing participants over time.
  • Weakened when participants drop out before study ends.
  • Cannot be completely eliminated from reserch, but should be considered within study, to hel pmeasure impact of mortality on future research.
Term
Hawthorne Effect
Definition
  • A participants personal attitude toward being involved in a study.
  • To control for this, researcher should offer comparable treatment to both control and experimental group, insuring that any difference is the result of an intervention and not personal attitudes.
Term
Placebo Effect
Definition
  • Caused by participants expectations rather than any intervention or treatment.
  • To control for placebo effect, the researcher should try to provide both the control and experimentation group with the the same information, insuring both groups have similiar expectations.
Term
Diffusion of Treatment
Definition
  • Occurs when treatment supplied to one group spills over and contaminates other groups.
  • Researchers should try to study groups with the least amount of day to day contact with each other.
  • It is also important to explain to participants the need to keep certain experiments confidential.
Term
Location Effect
Definition
  • Occurs when intervention locations differ and have a potential to effect outcome.
  • To control for location effect, the reasercher should make all efforts to create identical locations for various groups.
Term
Implementation Effect
Definition
  • Occurs when researcher inadvertently introduces bias or inequality to the study. Often when multiple people are involved in implementation of experiment, with varying levels of knowledge.
  • Whenever possible, someone other than program developer should present the program to participants. Pressenter should be as neutral as possible.
Term
Selection Treatment Interaction
Definition
  • First threat to external validity.
  • Concerns the degree to which a researcher can generalize the results of a study beyond a specific researched group.
  • Whether or not a study is randomized will determine how feasible and ethical it will be to generalize study results.
Term
Setting Treatment Interaction
Definition
  • Second threat to external validity.
  • The extent to which environmental conditions can be duplicated in further studies, and in other settings.
  • Reducing envionmental differences reduces chances that study results are effected by extraneous factors.
Term
History Treatment Interaction
Definition
  • Third threat to external validity.
  • Occurs when reseachers try to generalize findings to past and future situations.
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