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Internal vs. External Validity
Internal vs. External Validity
18
Education
06/13/2011

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Term
External Validity
Definition
The ability to generalize the study results to other groupsand settings beyond those in the current experiment.
Term
Internal Validity
Definition
Internal Validity exists if the observed effects of the independent variable on the dependent variable are real and not caused by extraneous factors.
Term
History Effect
Definition

threatens internal validity when events occur between the prestest and the posttest of a research study that could affect participants in such a way as to impact the dependent variable.

 

How to Control:

Have a control and an experimental group and compare the two at the end.

Term
Maturation effect
Definition

Threat to internal validity and occurs when when changes are seen in test subjects because of the time that has elapsed since the study began.

 

How To Control:

Have a control and an experimental group. At the end of the experiment study the results.

Term
Baseline
Definition

Threat to internal validity. The subject besing tested may learn how to do better on the test when they take it again. This is called being "test-wise."

 

How To Control:

Have a control group and do not give them any pre-test.

Term
Instrumentation
Definition

This is a threat to internal validity when measurements are not accurate or procedures are not standardized. The individual must be well trained to perform the tasks.

 

How To Control:

Make sure every subject is trained and make sure there are written directions for the subjects.

Term
Selection Bias
Definition

This is when subjects in either the control or the experimental group may have differences before the study actually starts. This could lead to differences being found in the actual study.

 

How To Control:

Recruit volunteers and randomly assign them groups. Matching people with select characterisitics also reduces selection bias.

Term
Selection Maturation Effect
Definition

This is a threat to internal validity. This occurs when intact groups vary in maturation level. One group could be more mature, more intellectual etc.

 

How To Control:

Pretest or prescreen groups on maturity levels before conducting an experiment.

Term
Statistical Regression
Definition

This occurs when participants in the study are selected based on their scores. These scores could be extrememly high or extrememly low.

 

How To Control:

Instead of selecting the students based on scores, select them randomly so that they aren't in groups based on testing.

Term
Mortality/Attrition
Definition

This occurs when a test subject in a long-term study becomes severly ill or passes away. Also some subjects could move away and not update contact information.

 

How To Control:

See how someone passing away affects the group. Also, be sure to require that all test subjects inform the researchers if they change address. 

Term
Hawthorne Effect
Definition

This occurs when a test subject changes the way they act or behave when they know they are being involved in a study.

 

How To Control:

One way to control this is to have a control group and provide them with special treatment. This will give both groups special attention. Researchers could also try and not inform the subjects that they are in an experiment.

Term
Placebo Effect
Definition

This is when a subjects expectations changes how they act rather than any provided treatment. This is strictly caused by expectations.

 

How To Control:

One way to control this is to make sure both the experimental and the control group will recieve the same thing. Another way to handle it is to give as little information as possible.

Term
Diffusion Effect
Definition

This occurs when the treatment being applied to one group spills over to another one.

 

How To Control:

One way to control this would be to pick subjects from completely different areas or backgrounds.

Term
Location
Definition

This occurs when there are differences in the locations where the interventions take place.

 

How to Control:

Keep the locations for all of the interventions the same.

Term
Implementation
Definition

This occurs when the people responsible for running the experiment may actually inadvertanly introduce inequality or bias to the experiment.

 

How To Control:

When this happens the best way to control it is to have someone other the person running the experiment present the program.

Term
Selection Treatment Interaction
Definition

This happens when a researcher involved ina study overgeneralizes the information that they gathered and believes it to be true for more people than it actually is.

 

How To Control:

In this case a person would want to use a smaller test selection and randomly select the test subjects.

Term
Setting Treatment Interaction
Definition

This occurs when an environment used in a study can be duplicated and can be used in other exxperiments.

 

How To Control:

Make sure that the environment can be duplicated when need be.

Term
History Treatment Interaction
Definition

This occurs when an experiment might be done at a peak time and the results may not be true if the study had been done at a different date.

 

How To Control:

Make sure to pick dates that could lead to similar results.