Part I.  Correlational versus Experimental Studies

Psychological studies vary in design. In correlational studies a researcher looks for associations among naturally occurring variables, whereas in experimental studies the researcher introduces a change and then monitors its effects. It is important to be able to distinguish between correlational and experimental designs, because only well-controlled experimental designs allow conclusions about cause and effect.

1.  A newspaper headline reads, Heavy Drinkers Get Lower College Grades. What would you conclude from this headline? What type of study was this based on?

 This study was most likely correlational because an experiment would not be ethical. (In order to do an experiment, the researcher would have to control the students' drinking, forcing some students to drink heavily and then observing the effects of the drinking on their grades.) All we can conclude from the headline is that heavy drinking is associated with lower grades. We cannot conclude that drinking caused the lower grades because other plausible interpretations have not been ruled out. (Perhaps students drink more because they make lower grades. Or perhaps drinking and grades appear related only because they are both related to the degree of student commitment to being in school.)

2.   People remember concrete words better than abstract ones. Could this finding have come from an experiment? Would it be reasonable to infer that concreteness facilitates memory?

Yes. An experiment could have been set up in two different ways. In one, called a between-subjects design, people are randomly assigned to groups. One group learns concrete words; the other learns abstract ones to see whether the group learning concrete words remembers more. In another experimental design, called a within-subjects design, all participants learn both the concrete and abstract words to see whether individuals learn concrete words better than abstract ones. (Of course, the order in which people learn the words would have to be controlled using a procedure called counterbalancing.

However, the two groups of words (concrete versus abstract) will probably also vary in others respects (such as word frequency). I.e., there are probably confounds, and hence, it is difficult to infer that concreteness alone facilitates memory.

3. Are people who were abused as children more likely than others to become child abusers? What type of study would be used to research this question?

 This question can only be addressed by correlational studies. (In order to do an experiment, the researcher would have to randomly assign some children to a group that gets abused; others to a group that does not get abused. Obviously, this cannot be done!) Thus, we must be cautious about assuming the cause of any association between experiencing abuse as a child and perpetrating it as an adult. Correlational studies do not support one interpretation over others.

4.  A health magazine reports that depressed people who continue medication for at least six months are less likely to relapse than are people who take medication for less than six months. What would you need to know about the design of this study, in order to interpret the report?

Enough information to see whether it was a correlational study or an experiment. In a correlational study, the researcher would take advantage of the fact that some depressed people stay on medication longer than others. (The researcher does not control how long people are on medication). Suppose the researcher finds that people on medication more than six months are less likely to relapse. The researcher cannot conclude that the increased time on medication improved the relapse rate because other explanations have not been ruled out. (Perhaps people who stay on medication longer differ from the others in ways that would protect them from relapse. Maybe the people on medication longer are also more likely to receive psychotherapy.)
In an experimental study, the researcher controls how long people stay on medication. Half of a sample of depressed people is randomly chosen to receive medication for less than six months; the others receive medication for more than six months. The only way the two groups differ is in the duration of the medication.

5.  A private school advertises that a group of their students recently scored 10 points higher on a math test than a group of other students from a public school? What can you conclude from this advertisment? Is this an example of an experiment?

 We cannot conclude anything about the cause of the difference in scores between the two groups. This is not an experiment because the researcher did not control group membership to ensure that the groups were roughly equivalent when they started school. (Imagine the reaction of parents if the researcher randomly assigned some children to attend private school and others to go to public school.). It is a quasi-experiment (resembles an experiment because it compares groups, but is not an experiment because the researcher did not control group membership) and should be interpreted like a correlational study. We cannot conclude that private school caused students to score higher on the math test. (Perhaps the students from private school are more likely to practice math on computer at home and it is this home activity, rather than experiences at school, that leads to the higher math scores.)

Part II.  Designing Research Studies in Psychology

1) A researcher, interested in the effects of unemployment on alcohol abuse, mailed questionnaires to the homes of workers recently laid off from a gold mine. Each participant was sent 10 questionnaires, one each month for 10 consecutive months. Participants were asked to anonymously fill out the questionnaires and return them. The questionnaires contained items pertaining to the amount of alcohol consumed daily before and after the layoffs occurred. Half of the subjects completed and returned all 10 questionnaires. For those individuals who returned all questionnaires, there was a positive correlation between alcohol consumption and length of unemployment, r=-.87 . That is, more alcohol was consumed as the period of unemployment progressed. In his report the researcher stated that "the conditions of unemployment produce a tendency for people to increase their alcoholic intake." Do you accept the researcher's conclusions? Why or why not?

 The researcher's conclusions are flawed for several reasons:

2) A counseling psychologist was interested in testing her hypothesis that physical exercise lessens depression. She was currently treating 39 people suffering from chronic depression, 36 of whom consented to participate in her study. She then assigned 12 people to each of 3 conditions. People in condition I were asked to exercise outdoors at least 3 times per week, people in condition II at least 5 times per week, and people in condition III were not asked to exercise but were asked to spend some time outdoors at least 3 times a week. At the end of the six weeks, each was assessed for depression. People in each of the conditions were now less depressed than at the outset of the experiment, and, in addition, people in conditions I and II were significantly less depressed than people in condition III. Level of depression was equal in conditions I and II. The researcher concluded that exercise helps depression above and beyond improvement due to spending time outdoors. She also concluded that 3 times a week was enough to benefit the depressed person. Before you evaluate the validity of these conclusions, what other details should you know about this study?

You would need to know

3) A school psychologist wondered whether students would perform better on tests when listening to music. On the first day of exams, students listened to music in the morning while they wrote their history test and then wrote their math test in the afternoon in a quiet room. The average score on the math test was 79% and was significantly greater than the average of 68% on the history test. The psychologist concluded that music does not help exam performance, but, in fact, hinders it. Why would you not trust his conclusions?

 His conclusions are flawed because

4) A developmental psychologist observed children who attended daycare at least 30 hours per week and compared their behavior to their peers being raised at home. The psychologist found that the daycare children scored significantly higher than the other children on a measure of aggression. Could the psychologist conclude that daycare makes children aggressive? Why or why not?

 No. This is not a true experiment because the psychologist did not manipulate the independent variable (i.e., control who went to daycare and who stayed home). This is an example of a quasi-experiment because subjects determine their own group membership, rather than being randomly assigned to groups. Perhaps the groups differ in other ways and these other ways affect aggression. For example, perhaps the parents of daycare children are more impatient with their children and it is parent impatience that increases aggression in the children rather than the daycare experience per se. The problem with a quasi-experiment is that it does not allow us to prove one hypothesis over others.

5) An advertisement asks for subjects in a psychology experiment. The first 50 responders into group #1 that gets a "smart pill", the second 50 go into group #2 which gets no pill.  After a while the experimenter measures the IQ of each group and finds that group #1 has a higher average IQ. Can the research conclude that te pill makes people smarter?  Why or why not?

No. The two groups differ in at least two ways. First, the two groups need to be equated in terms of their treatment -- both should receive a pill (one the actual drug, the other an inert substance), neither group should know which pill they are receiving (to reduce subject expectancies), and the experimenter (or at least the IQ test giver/score) should not know which pill each subject received (to eliminate experimenter expectancies). Second, the two groups may differ in terms of IQ before even receiving the drug. Maybe highly motivated, academically orientated, individuals rushed to sign up for the experiment, and hence the first group may have a higher IQ to begin with. Subjects should have been randomly assigned to the two groups to reduce the effects of individuall differences.