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A study that does a good job controlling for the possible effects of extraneous variables.
Researcher should control the study to eliminate as much as possible extraneous factors. |
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is threatening to internal validity when events occur between the pretest and posttest of a research study that could affect participants in such a way as to impact the dependent variable.
Have a control group and be sure not to have that group exposed to the same treatment as the experimental group |
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| A group of participants exactly like the treatment group in every way possible but for the lack of treatment. |
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| The group receiving treatment. |
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Changes seen in subjects because of the time that has elapsed since the study began and which aren't the result of any program effects.
Use of a control group would eliminate this. |
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| a measurement taken to obtain the status or level of a variable prior to initiating a study |
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Any differences seen from baseline to posttest may be from a testing effect and not the independent variable.
Use of a control group that does not receive any pretesting will fix |
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The instrumentation used to collect data in a study can cause threats to internal validity when measurements are not accurate or procedures are not standardized.
Carefully designed instruments reduce the threat |
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when individuals are selected in a nonrandom manner.
Randomly assigning volunteers to groups is better than allowing the to self-select. Match participants on selected characteristics and then randomly assinging them to groups and also pretesting groups on measure of the dependent variable to make sure there are no pretreatment differences. |
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| Selection maturation effect |
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Occurs when intact groups that vary in their maturation level.
Prescreen and pretest groups on maturity levels. |
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occurs when participants are selected on the basis of their extremely high or low scores.
The study should be designed to follow a random sample |
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| Attrition creates a mortality effect-- loss of subjects to death or poverty or drop out and the number of participants sinks to below established guidelines of statistical analysis. |
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When participants attitudes toward being involved in a study affect the way they behave.
Try to provide the control group with some type of special treatment that is comparable to the experimental group but would not have a direct impact on the dependent variable. |
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| Caused by the participants expectations rather than by any provided treatment. Similar to the Hawthorn effect, but that the threat is caused by expectations. |
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Occurs when treatment being applied to one group spills over or contaminates another group.
Use another control group and pay careful attention that they are similar to the group being studied |
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Occurs when there are differences in the locations where interventions take place
The best way to control for a location effect is to make the location the same for all participants. |
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When the individual(s) responsible for implementing the experimental treatment and the possibility that they may introduce inequality or bias into the study. Two ways this can happen: multiple people providing the treatment program or intervention and they may not be equal in their knowledge levels, understanding of the program, personality traits, presentation skills, etc. The second way is if an individal implementing the intervention inadvertently favors one group over another.
Someone other than the program developer should present the program |
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| A study that does a good job being relatable in setting and to people more widely than just to the study group. |
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| Selection Treatment Interaction |
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about the ability of the researcher to generalize the results
be careful of over generalization to groups for whom the study results might not apply |
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| The experimentally accessible population |
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| Setting Treatment Interaction |
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| The extent to which the environmental conditions or setting under which an experimental study was conducted can be duplicated in other settings. |
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| History Treatment Interaction |
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| develops when the researcher tries to generalize findings to past and furture situations. Some experiments may be time-sensitive and may not produce similar results if conducted earlier or later. |
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