Has the control group been contaminated in some way? Sometimes the treatment and control group participants are able to communicate with each other. The danger is that some aspects of the experimental stimulus (i.e., the intervention) are passed on from the treatment group to the control group (e.g., methods, materials, perspectives, etc.); that is, there is an exchange of information between the groups, which influences the behaviour of the control group. If this is the case, the control group may not be an actual control group. As a result, the scores on the dependent variable that is being measured are more likely to be similar between the groups. This is known as diffusion or imitation of treatments, resulting from an exchange of information between groups.
There are many factors that can lead to cross-contamination between the treatment and control group (e.g., an increased time between the pre-test and post-test; greater homogeneity between the sample/participants that may result in their interacting outside of the research process, such as their sharing similar social groups, their being geographical closeness between participants, and so forth).
In experimental and quasi-experiment research designs where there is a treatment and control group, participants can sometimes become competitive when not included in the treatment group. As a result, they exert additional effort, which may improve the score on the dependent variable for the control group compared with normal conditions (i.e., compared with what is typical or expected for such a group). This can even happen when there are two treatment groups and no control group, so long as one of the groups is receiving a less attractive treatments/intervention. It is known as compensatory rivalry (or compensatory equalization of treatments). Imagine the following scenarios:
Study #5
The introduction of new work methods designed to increase employee performance
The John Henry effect concerns a steel worker, John Henry, who was aware that his output was going to be compared to a steam drill. As a result, he put in extra effort, but whilst managing to outperform the steam drill, the overexertion led to his death (Cook and Campbell, 1979, p. 55). Similarly, you could be examining how a new process in an organisation could reduce the requirement for manual labour. In comparing the treatment group using the new process with the control group, it is possible that the control group would work additionally hard for the period of the experiment in order to reduce the risk of losing their jobs. This could occur in a number of potential change situations.
In such cases, members of the control group try to compensate for the fact that they are missing out on the experiment treatment by working/trying/concentrating harder.
Demoralization (or resentful demoralization; and in some cases, compensatory demoralization) can happen in experimental research when participants are assigned to the control group rather than the treatment group. This is not always the case, especially where there are no negative outcomes associated with control group membership. However, there are instances where being assigned to the control group can be viewed to be negative, leading to feelings of anger, demoralization, resentment, neglect, amongst other negative feelings.
Demoralization is a threat to internal validity when it:
Results in increased dropout rates because participants simply give up, especially amongst control group members, creating similar problems to experimental mortality; and/or
The difference in the scores on the dependent variable between the two (or more) groups is increased (i.e., artificially) compared with what would have been expected.
Imagine the following study:
Study #6
The impact of team away days on employee motivation
The experiment: A firm wants to understand the impact of team away days (i.e., the independent variable) on employee motivation (i.e., the dependent variable). Team away days, which are basically 'team building' exercises, ranging from paintballing to creative challenges, and even wine tasting, are expensive, so the firm wants to know if they are worthwhile. To test the impact of team away days of employee motivation, the firm randomly assigns employees into two groups. One group does not go on the team away day (i.e., the control group), whilst the other group goes on the away day (i.e., the treatment group). The pre-test consists of a questionnaire that employees from both groups take, which measures employees? level of motivation. When the employees that go on the team away day return, they re-take the employee motivation survey. This provides the post-test scores on the dependent variable (i.e., employee motivation). The aim is to compare the scores between the two groups on the dependent variable to see if there are any differences. However, irrespective of the results of the experiment, a threat to internal validity has entered the experiment: demoralization. After all, to avoid selection bias [see the section: Selection biases and internal validity], employees are randomly assigned to the treatment group and control group.
However, since employees are assigned to the treatment and control groups randomly rather than based on their performance; that is, employees are not selected as a reward (or bonus) because they have performed well in their jobs, this can cause a problem. It can cause a problem if employees in the control group see selection for the team away day (i.e., the treatment group) as being a privilege (or bonus), since they may resent not receiving the privilege/bonus (i.e., why this threat to internal validity is sometimes called resentful demoralization or compensatory demoralization).
Sometimes you will choose (or need) to compensate participants to encourage them to take part in your research. Broadly, such compensation can be viewed as either general compensation or control group compensation:
General compensation
All participants are rewarded simply for taking part, irrespective of whether they are in the control group or the treatment group. For example, study participants may be given money, physical items (e.g., clothes; iPod, etc.), or some other form of compensation if they complete an online survey or take part in a physiological or psychological experiment. Whilst these forms of general compensation may affect the control group and treatment group equally, the can reduce the internal validity of your study because they can lead to selection biases [see the section: Selection biases and internal validity].
Control group compensation
The control group sometimes misses out on a treatment, which leads to the demoralization (or resentful demoralization; and in some cases, compensatory demoralization) that we discussed in the previous section [see the section: Demoralization and internal validity]. This can lead to a concern amongst researchers, whether because of the threat to internal validity that this causes, or a general sympathy with the control group members. When this happens, researchers can feel pressured to provide the control group with compensation that the treatment group does not receive. This may be general compensation for taking part, as discussed above, or it may be another form of compensation. For example, Babbie (2010) illustrates this in a hospital environment, suggesting that hospital staff may provide control group members with ?additional tender loving care? (Babbie, 2010, p.242) because they feel sympathy for control group members. You can imagine how this may be the case in drug trials where seriously ill patients do not receive the potentially lifesaving drug because they have been assigned to the control group. However, the problem with this form of one-sided compensation is that the control group is no longer a control group in the true sense of the word because they have still been compensated in some way. This could affect the differences in the scores on the dependent variable between the control group and treatment group, reducing the internal validity of the study.