Chapter 16. How Would You Know How Well Antidepressants Work?

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C. Nathan DeWall, University of Kentucky

David G. Myers, Hope College

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Note: You will be guided through the Intro, Design, Measure, Interpret, Conclusion, and Quiz sections of this activity. You can see your progress highlighted in the non-clickable, navigational list at the right.

Watch this video from your author, Nathan DeWall, for a helpful, very brief overview of the activity.

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So, how would you know how well antidepressant drugs work? To study this question effectively in your role as researcher, you need to DESIGN an appropriate study that will lead to meaningful results, MEASURE depressive symptoms, and INTERPRET the larger meaning of your results, considering how your findings would apply to the population as a whole.

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Case Studies:

Experiments:

Correlational Studies:

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You have chosen a Case Study design. In a Case Study design, you will choose one person or a small group of people and study them in depth.

As a reminder, major depressive disorder is the diagnosis given when a person’s feelings of depression meet the clinical criteria.

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What can we learn from these participant choices?

A small group of people who eat at restaurants every night. This option does not tell you about your participants’ weight or the size of the dinner plates they use. To know whether using larger dinner plates make us fat, you would need to study a group of individuals who have average body weight. This way you can determine whether changing the size of the plates they use causes them to behave in ways that will increase their weight.

A small group of people who are obese. This option tells you about your participants’ weight but not about the size of the dinner plates they use. To know whether using larger dinner plates makes us fat, you would need to study a group of individuals who have average body weight (not just people who are obese), and then vary the size of the dinner plates they use to see if that causes them to increase their weight.

A small group of people who are thin. This option tells you about your participants’ weight but not about the size of the dinner plates they use. To know whether using larger dinner plates makes us fat, you would need to study a group of individuals who have average body weight (not just people who are thin), and then vary the size of the dinner plates they use to see if that causes them to increase their weight.

A small group of people who have average body weight. You were right to choose people who have average body weight, but this option doesn’t tell us about the size of the dinner plates they use. To know whether using larger dinner plates makes us fat, you would need to study a group of individuals who have average body weight, and then vary the size of the dinner plates they use to see if that causes them to increase their weight. Also, you would need to study a large group, not a small group as in this Case Study approach, in order to determine whether the idea of using larger dinner plates making us fat may apply to the larger population.

Trying to choose a sample of participants helps us realize that the CASE STUDY IS NOT THE BEST RESEARCH DESIGN to test this question. We’d get more helpful results by studying large groups of people with major depressive disorder who are not yet taking any medication designed to improve their mood. This would help us determine how well antidepressants work.

Click “Next” to go back and try again to select the most effective research design.

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You have chosen a Correlational design, which means you want to examine the relationship between two or more variables. For example, suppose researchers are interested in knowing whether people with high levels of depression also have high levels of anxiety. To answer this question, researchers would measure participants’ depressive symptoms and anxiety levels to determine if there is a relationship between these two factors. (There is.)

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You might correlate depressive symptoms with how frequently people take antidepressants. The result would tell you if regularly taking antidepressants relates to fewer depressive symptoms, but it would not tell you anything about whether the antidepressants are actually having an effect. A correlational design would not allow us to rule out the placebo effect, where results are observed based on expectations alone. To know how well antidepressants work, you would need to systematically assign some people with depression to take an antidepressant and others to take a placebo pill. Then you could compare depressive symptoms between the two groups.

So, CORRELATIONAL IS NOT THE BEST RESEARCH DESIGN for this study.

Click “Next” to go back and try again to select the most effective research design.

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Nice work! You have correctly chosen to use an Experimental design for your study. Next, you need to choose the most appropriate participants for your study.

As a reminder, major depressive disorder is the diagnosis given when a person’s feelings of depression meet the clinical criteria.

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You chose A group of people who take antidepressants and have a family history of depression, but this is NOT CORRECT.

This is not the best option, because you do not have any specific information about whether participants have major depressive disorder. People with a family history of depression do not necessarily develop major depressive disorder. You also can’t test how well antidepressants work if your study participants already take them.

Click “Next” to try again to choose the most appropriate participants for your study.

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You chose A group of people who were formerly depressed, but this is NOT CORRECT.

Just as fully rested people do not need a nap to treat their lack of tiredness, people who are no longer depressed do not need to take medication.

Click “Next” to try again to choose the most appropriate participants for your study.

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You chose A group of people with major depressive disorder who believe strongly that antidepressants are ineffective in reducing depressive symptoms, but this is NOT CORRECT.

It would be better to study a group of people who have varying attitudes about the effectiveness of antidepressants. To know how well antidepressants work, you would need to study people with major depressive disorder who have a variety of opinions about the effectiveness of medication.

Click “Next” to try again to choose the most appropriate participants for your study.

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Good job! You have correctly chosen to use an Experimental design. You also chose an appropriate sample of participants—A group of people with major depressive disorder who are not currently taking medication to treat their depression. For effective results, you will want to randomly assign some people to take an antidepressant and others to take a placebo pill, and then compare depressive symptoms between the two groups.

Now you need to determine how best to MEASURE the relevant behavior or mental process, which in this case is depressive symptoms.

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You chose Have participants draw a picture of two people having a conversation. Score the picture in terms of how happy or sad the two drawn people look, but this is NOT CORRECT.

This would not be the best option, because this would not be considered a valid and reliable instrument for testing participants’ depressive symptoms. To know how well antidepressants work, we would need to measure participants’ depressive symptoms using an established, effective assessment tool.

Click “Next” to try again to select the best way to measure depressive symptoms.

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You chose Have participants complete a valid and reliable questionnaire that measures their parents’ depressive symptoms, but this is NOT CORRECT.

You were right to choose a valid and reliable assessment instrument, but in this case you would not be gaining any direct information about participants’ depressive symptoms. You would learn about participants’ parents, but you wouldn’t know anything about participants’ own depressive symptoms. To know how well antidepressants work, we have to know how participants rate themselves on a variety of depressive symptoms.

Click “Next” to try again to select the best way to measure depressive symptoms.

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You chose Measure participants’ heart rate, breathing ability, and stress hormones, but this is NOT CORRECT.

With this option, you would not receive any direct information about participants’ depressive symptoms. These physiological measures might relate to depressive symptoms, but they also relate to several other behaviors and mental states unrelated to depression. To know how well antidepressants work, we have to know how participants rate themselves on a variety of depressive symptoms.

Click “Next” to try again to select the best way to measure depressive symptoms.

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Nice job! You have correctly chosen to use an Experimental design. You chose an appropriate sample of participants—a group of people with major depressive disorder who are not currently taking any medication to treat their depression. You also chose how best to MEASURE the relevant behavior or mental process, which in this case is depressive symptoms. You selected the option, Have participants complete a valid and reliable questionnaire that measures their depressive symptoms. It’s important to use an assessment instrument that is both valid and reliable.

Several studies have examined how well antidepressants work to reduce depressive symptoms. In one analysis of over 170 studies using 23,000 depressed patients, antidepressants reduced depressive symptoms (Kahn et al., 2012). Other research has shown that people with major depressive disorder who received both antidepressants and psychotherapy benefited more than did people who received only antidepressants. So, we have some clear evidence that antidepressants are effective in reducing depressive symptoms, especially when combined with psychotherapy.

Knowing this, you need to consider how you can apply what you’ve learned to the larger population—beyond the people you’ve studied. Consider where you might encounter roadblocks to confidence in your results. What factors might keep you from being able to apply what you’ve learned in a broader context?

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You tested how well antidepressants work to reduce depressive symptoms. You recruited a sample of participants with major depressive disorder who were not currently taking antidepressants. You randomly assigned some participants to take antidepressants, and other participants to take placebo pills. Next, you measured and compared participants’ depressive symptoms. Several factors may influence your study results, and they might not have any relation to whether your participants took the antidepressants or placebo pills! Factors that could interfere with our INTERPRETATION of results are called confounding variables.

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Confounding Variables:

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The confounding variables for your study would include those highlighted below:

To have the most confidence in your results, you need to keep track of the highlighted confounding variables. We need to know whether participants follow the schedule for taking their antidepressants or placebo pills. If some people stop taking their medication and we do not know, we might draw incorrect conclusions about how well antidepressants work. We also need to know whether people began the experiment with extremely severe depressive symptoms, because antidepressants’ effectiveness varies depending on severity of participants’ symptoms—with the greatest effects for those who are very severely depressed (Fournier et al., 2009). Psychotherapy can also reduce depressive symptoms, so we need to keep track of whether participants are currently receiving psychotherapy.

Note that by randomly assigning participants to either the antidepressant or placebo condition, you control for many other possible confounding variables. With random assignment, each participant has the same chance of being assigned to each group. This should give each of your groups a balanced number of participants expressing these variations.

Click on "Video Hint" below to see a brief animation describing Random Assignment.

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Random Assignment:

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You may do better on the Quiz if you take notes while watching this video. Feel free to pause the video or re-watch it as often as you like.

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