Contrast the strengths and weaknesses of dealing with nonspuriousness through statistical control and through randomization.

Question

What will be an ideal response?

Answer 1

Strengths: Experimental research provides the most powerful design for testing causal hypotheses because it allows us to confidently establish the first three criteria for causality—association, time order, and nonspuriousness. True experiments have at least three features that help us meet these criteria:
1. Two comparison groups—one receiving the experimental condition (e.g., treatment or intervention), termed the experimental group, and the other receiving no treatment/intervention or another form thereof, termed the control group.
2. Random assignment to the two (or more) comparison groups.
3. Assessment of change in the dependent variable for both groups after the experimental condition has been applied. This is usually called a posttest.
We can determine whether an association exists between the independent and dependent variables in a true experiment because two or more groups differ in terms of their value on the independent variable. One group, the experimental group, receives some “treatment” that is a manipulation of the value of the independent variable. In a simple experiment, there may be one other group that does not receive the treatment; it is termed the control group or comparison group.
First, it is crucial that the two groups be more or less equal at the beginning of the study. If you let students choose which group to be in, the more violent students may pick the violent movie, hoping, either consciously or unconsciously, to have their aggressive habits reinforced. If so, your two groups won’t be equivalent at the beginning of the study. As such, any difference in their aggressiveness may be the result of that initial difference (a source of spuriousness), not whether they watched the violent video. You must randomly sort the students into the two different groups. You can do this by flipping a coin for each one of them, pulling names out of a hat, or using a random number table as described in the previous chapter. In any case, the subjects themselves should not be free to choose nor should you (the experimenter) be free to put them into whatever group you want.
Note that the random assignment of subjects to experimental and comparison groups is not the same as random sampling of individuals from some larger population (see Exhibit 6.5). In fact, random assignment (randomization) does not help at all to ensure that the research subjects are representative of some larger population; instead, representativeness is the goal of random sampling. What random assignment does—create two (or more) equivalent groups—is useful for ensuring internal validity, not generalizability.
Next, people in the two groups will interact among themselves. Then, the control group will watch a video about gardening while the experimental group will watch a video featuring a lot of violence. Next, both groups will sit and interact again among themselves. At the end, the interactions within both groups before and after the videos will be coded and you will see whether either group increased in aggressiveness. Thus, you may establish association.
Weaknesses: Quasi-experiments are weaker than true experiments in establishing the nonspuriousness of an observed association—that it does not result from the influence of some third, uncontrolled variable. On the other hand, because these quasi-experiments do not require the high degree of control necessary in order to achieve random assignment, they can be conducted using more natural procedures in more natural settings, so we may be able to achieve a more complete understanding of causal context. In identifying the mechanism of a causal effect, though, quasi-experiments are neither better nor worse than experiments.