Internal.

Could ultimately impact the dependent variable, when event occur to the participants of a study between the pretest and posttest.

Can be controlled by ensuring there is a control group and an experimental group. 

Internal.

Changes that occur to a participant between the beginning and ending of a study that may result other than the programs effects.

This can be controlled with a control group.

Internal.

A possible discrepency between the pretest and posttest results because a participant's ability to be "test-wise" and anticipate the questions of a posttest.

This can be controlled with a control group who does not take part in a pretest.

Internal.

Can cause a threat to internal validity when measurements are not accurate or procedures are not standardized. 

To control this potential threat would be to ensure well-designed instruments are used.

Internal.

Occurs when individuals are selected in a nonrandom manner.

Can be controlled by recruiting volunteers and then randomly assigning them to groups is better than allowing volunteers to self-select a group. Matching participants on selected characteristics and then randomly assigning them to groups. Pretesting groups on measures of the dependent variable to make sure there are no pretreatment differences between groups. 

Internal.

Occurs when using intact groups that vary in their maturation level.

Can be controlled by pretesting and/or prescreening groups on their maturity levels.

Internal.

Occurs when participants are selected on the basis of their extremely high or low scores. Those who first score high, will then score lower and those who first scored lower will score higher.

This can be controlled by designing the study to simply follow a random sample rather than placing participants in high and low groups based on one testing. 

Internal.

Occurs in long-term longitudinal studies, when participants die or are ill. Can also occur when participants move and contact information is not updated or when participants choose to no longer participate in the study before it's completed.

Can be controlled by oversampling and using large group sizes is one way to overcome small group size after mortality. Using incentives can curb drop out rates. 

Internal.

Occurs when participants change the way they behave because they know they are being observed.

Can be controlled by providing the control group with some type of special treatment that is comparable to the experimental group but would not directly impact the dependent variable. Can also be controlled by omitting information about what is being observed to the participants. 

Internal.

Occurs when participants have certain expectations of the treatment. 

Can be controlled by ensuring both the control and experimental group both receive the same information prior to the study. Can also be controlled by omitting details of the study to both groups. 

Internal.

Occurs when the treatment being applied to one group spills over or contaminates another group. 

Can be controlled by using a control group from another location and look for similarity between the experimental and control group to aid the balance between groups. If that is not possible, ensure the participants keep their results confidential from other participants. 

Internal.

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

Can be controlled by ensuring that the location is the same for all participants. If not possible, researcher is to try to minimize as many differences as possible.

Internal.

Occurs when an individual or individuals implementing the experimental treatment and the possibility that they may inadvertently introduced inequality or bias into the study.

This can be controlled by having someone else other than the researcher present the program. Can also be controlled by having a neutral observer watch the presenter with specific instructions to look for ways in which the two groups are being treated differently. The neutral observer provides feedback to avoid bias.

External.

Occurs when the researcher's ability to generalize the results of a study go beyond the groups involved in the study.

Might be controlled by not overgeneralizing the groups.

External.

The ability that environmental conditions or setting of an experimental study can be replicated in other settings.

Might be controlled by ensuring similarities amongst groups being compared (i.e. SES, cultural climate).

External.

Occurs when generalizing findings to past and future situations.

Might be controlled by being aware of one's timing of research and the effects it may have on the study's participants.