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Researchers wanted to test whether a new drug therapy results in a more rapid response in patients with major depression. To do this, they recruited 63 inpatients with a diagnosis of major depression. Patients were randomly assigned to two treatment groups receiving either placebo (31 patients) or the new drug therapy (32 patients). The response variable was the Hamilton Rating Scale for Depression score. After collecting and analyzing the data, it was concluded that the new drug therapy is effective in the treatment of major depression. (Source: "Metyrapone as Additive Treatment in Major Depression," Holger Jahn, MD; et al.; Archives of General Psychiatry, \(61(2004): 1235-1244\) ) (a) What type of experimental design is this? (b) What is the population that is being studied? (c) What is the response variable in this study? (d) What is the factor? What are the treatments? (e) Identify the experimental units. (f) Draw a diagram similar to Figure 6 or 7 to illustrate the design.

Step by step solution

01

- Identify the Type of Experimental Design

The experiment involved randomly assigning patients to one of two treatment groups (placebo or new drug therapy). This indicates a Randomized Controlled Trial (RCT) design.

02

- Determine the Population Being Studied

The population includes all inpatients with a diagnosis of major depression who could potentially be recruited for the study. In this case, 63 inpatients with major depression were studied.

03

- Identify the Response Variable

The response variable is the outcome measured to determine the effect of the treatments. In this study, it is the Hamilton Rating Scale for Depression score.

04

- Define the Factor and Treatments

The factor is the variable that the researchers manipulate, which is the type of treatment (type of drug therapy). The treatments are the placebo and the new drug therapy.

05

- Identify the Experimental Units

The experimental units are the 63 inpatients with major depression who were randomly assigned to the treatment groups for the study.

06

- Draw a Diagram of the Design

A diagram would show the 63 patients being randomly divided into two groups: one receiving the placebo (31 patients), and the other receiving the new drug therapy (32 patients).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

randomized controlled trial

A randomized controlled trial (RCT) is a type of scientific experiment. It aims to reduce bias when testing the effectiveness of new treatments. In an RCT, participants are randomly allocated to one of two or more groups. One group receives the treatment under study; another group receives a control, such as a placebo or standard treatment. Randomization helps ensure that groups are similar in all respects except for the treatment. This increases the likelihood that differences in outcomes between groups are due to the treatment. In the exercise, researchers conducted an RCT by randomly assigning 63 inpatients with major depression to receive either the new drug therapy or a placebo.

response variable

The response variable is the outcome measured in an experiment. It shows the effects of the treatments. In the major depression study, the response variable is the Hamilton Rating Scale for Depression score. This scale measures the severity of a patient’s depression. By comparing these scores between the treatment and placebo groups, researchers can determine the effectiveness of the new drug.

treatment groups

Treatment groups are the different groups in an experiment that receive different treatments. In an RCT, participants in one group receive the new treatment, while others may receive a placebo or standard treatment. Treatment groups allow researchers to compare the effects of different interventions. In the exercise, the researchers had two treatment groups: one received the new drug therapy, and the other received a placebo. This setup helps in comparing the effectiveness of the new drug against a control.

experimental units

Experimental units are the smallest divisions of the sample that receive treatments independently. In other words, they are the subjects or objects being studied. In human studies, they are often the individual participants. In the major depression study, the experimental units are the 63 inpatients, because each patient received either the placebo or new drug therapy. Analyzing outcomes from these units helps researchers draw conclusions about the treatment's effectiveness across the sample.

population and sample

In experimental design, the population is the entire group of individuals or instances about which we hope to learn. The sample is a subset of the population that is actually observed and analyzed to draw conclusions about the population. In the study mentioned, the population is all inpatients with major depression who could potentially partake in such a study. The sample of this population is the 63 inpatients who were actually recruited and participated in the trial. Researchers use samples because studying the entire population is usually impractical. Careful sampling and analysis help ensure that the findings can be applied to the larger population.