- This happens when an event, occuring between the pretest and posttest, affects the participants which impacts the dependent variable .

Solution: Use a control group that receives no treatment

-this happens when changes are seen in subjects because of the amount of time that has passed and not because of the program. (older, wiser, stronger)

Solution:Use a control group that receives no treatment

-this happens when participants being tested may learn how to do better on the test the second time they take the test.

Solution:Use a control group that does not receive pre-testing.

-This happens when the instrumentation used to collect data in a study are not accurate or procedures are not standardized or not calibrated.

Solution People using equipment should be trained and consistent. -Well-designed instruments can reduce this threat

- This happens when individuals are selected in a nonrandom manner.

Solution: Recruit volunteers then randomly assign them to groups

-matching participants on selected characteristics and then randomly assign them to groups

-Pre-testing groups on measures of the dependent variable to make sure there are no pretreatment differences between groups.

-This happens when using intact groups that vary in their maturation level.

Solution: Pre-testing and/or prescreening groups on maturity levels

- This happens when those who score super high on a test have nowhere to go except down, and those who score super low have nowhere to go but up.

Solution: the study could be designed to follow a random sample of participants representing the full range of scores rather than placing participants in high and low groups based on one testing.

- This happens when participants die, move, are too sick to complete study, or will drop out.

Solutions: Oversampling and using large group sizes (doesn‘t eliminate difference in drop out participants and ones that stay)

-Using incentives to encourage participants to stay in the study may be helpful.

-Obtaining good demographic information about study participants at the beginning of the study and then determining if the group makeup has changed at the end of the study after mortality has occurred

-this happens when a participant’s attitude towards being involved in the study affects the way they behave.

Solution: 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.

-Keep participants from knowing that they are taking part in a study or being observed. (may not be ethical)

- This happens when participants expectations may affect the results.

Solution:When testing new drugs a control group is used that receives a placebo (blind study, if the researcher also doesn‘t know double blind)

-Both the control and experimental groups receive the same information or very little information for similar expectations.

-This happens when the treatments being applied to one group spills over another group.

Solution:Use a different community for the control group.

-Inform participants to keep treatments confidential until the end of the study period.

-This happens when there are differences in the locations where interventions take place and the location might have an impact on the effectiveness.

Solution: Make locations the same for all participants or do everything possible to minimize differences between the locations.

- This happens when someone responsible for implementing the experimental treatment and the possibility that they may inadvertently introduce inequalities or bias into the study. (multiple people with different levels of knowledge)

Solution: Trying to make sure that all persons responsible for implementing the program are equally trained and competent

- This happens when the ability if the researcher to generalize the results of a study beyond the groups involved in the study.

Solution: Results can be generalized to a group when a random sample of participants is used.

- This happens when the researcher tries to generalize findings to past and future situations. Some experiments may not produce the same results if conducted earlier or later.

Solution:Be sure to duplicate setting and historical factors as nearly as possible when replicating a program with a different population.

- This happens when someone responsible for implementing the experimental treatment and the possibility that they may inadvertently introduce inequalities or bias into the study. (Individual implementing instrument favors one group)

Solution: Have someone other than the program developer present the program (neutral) or have a neutral observer watch the presentations to provide feedback while the program is ongoing.