91Ó°ÊÓ

Depression Researchers wanted to compare the effectiveness and safety of an extract of St. John's wort with placebo in outpatients with major depression. To do this, they recruited 200 adult outpatients diagnosed as having major depression and having a baseline Hamilton Rating Scale for Depression (HAM-D) score of at least \(20 .\) Participants were randomly assigned to receive either St. John's wort extract (900 mg/d for 4 weeks, increased to \(1200 \mathrm{mg} / \mathrm{d}\) in the absence of an adequate response thereafter) or a placebo for 8 weeks. The response variable was the change on the HAM-D over the treatment period. After analysis of the data, it was concluded that St. John's wort was not effective for treatment of major depression. (Source: "Effectiveness of St. John's Wort in Major Depression," Richard C. Shelton, MD; et. al.; Journal of the American Medical Association \(285(2001): 1978-1986)\) (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 experimental design

This is a randomized controlled trial (RCT) design. Participants are randomly assigned to either the treatment group (receiving St. John's wort) or the control group (receiving placebo).

02

Determine the population studied

The population being studied includes adult outpatients diagnosed with major depression and a baseline Hamilton Rating Scale for Depression (HAM-D) score of at least 20.

03

Specify the response variable

The response variable is the change in the Hamilton Rating Scale for Depression (HAM-D) score over the treatment period.

04

Identify the factor and treatments

The factor in the study is the type of treatment administered to the participants. The treatments are: 1) St. John's wort extract (900 mg/day for 4 weeks, increased to 1200 mg/day in the absence of an adequate response) and 2) placebo.

05

Identify the experimental units

The experimental units in this study are the 200 adult outpatients who are diagnosed with major depression.

06

Illustrate the experimental design

A diagram illustrating the experimental design would look like this: 1. Selection: 200 adult outpatients diagnosed with major depression and HAM-D score ≥ 202. Random Assignment: - Group 1: St. John's wort (900 mg/day, potentially increasing to 1200 mg/day) - Group 2: Placebo 3. Outcome Measurement: Change in HAM-D score over the 8-week treatment period

Unlock Step-by-Step Solutions & Ace Your Exams!

• Full Textbook Solutions

  Get detailed explanations and key concepts

• Unlimited Al creation

  Al flashcards, explanations, exams and more...

• Ads-free access

  To over 500 millions flashcards

• Money-back guarantee

  We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!

Key Concepts

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

Experimental Design

An experimental design is a structured approach to testing hypotheses under controlled conditions to draw conclusive results. In this study, researchers employed a **randomized controlled trial (RCT)**. This means participants were randomly assigned to different groups to compare the effects of St. John's wort against a placebo. The random assignment helps ensure that differences observed are due to the treatment rather than other variables.
Key features of an RCT include:

• Random assignment to treatment or control groups
• Controlled conditions to minimize bias
• Comparison between the experimental treatment (St. John's wort) and control (placebo)

This design helps validate the effectiveness and safety of new treatments.

Response Variable

The response variable in an experimental study is the outcome that researchers measure to determine the treatment's effect. In this particular study, the response variable was the **change in the Hamilton Rating Scale for Depression (HAM-D) score** over the 8-week treatment period. The HAM-D score is a common way to measure the severity of depression symptoms.
The change in this score from the beginning to the end of the study indicates whether the depression symptoms improved, worsened, or remained the same. By comparing these changes between participants receiving St. John's wort and those receiving placebo, researchers can infer the effectiveness of the treatment.

Treatment Groups

In a randomized controlled trial, different groups receive different treatments to compare their effects. In this study, there were two primary **treatment groups**:

• **Group 1 (Treatment Group)**: Participants receiving St. John’s wort extract. They initially received 900 mg per day for 4 weeks, and if there was no adequate response, the dose was increased to 1200 mg per day.
• **Group 2 (Control Group)**: Participants receiving a placebo. This group did not receive any active medication, just a substance with no therapeutic effect.

The comparison between these groups helps determine if the treatment (St. John’s wort) has a real effect on reducing the symptoms of major depression when compared to no treatment (placebo).

Population Studied

The population studied in an experiment refers to the broader group that researchers aim to learn about through their sample. In this study, the **population studied** includes **adult outpatients diagnosed with major depression** who have a baseline Hamilton Rating Scale for Depression (HAM-D) score of at least 20.
This specific population was chosen to ensure that those participating had a significant level of depression, making it possible to measure any meaningful changes brought about by the treatment. The findings from this sample can, to some extent, be generalized to all adults with major depression, assuming the sample is representative.

Random Assignment

Random assignment is a crucial aspect of experimental design, particularly in randomized controlled trials. **Random assignment** means that participants are allocated to different treatment groups purely by chance. This methodology helps reduce selection bias and ensures that each group is comparable at the start of the treatment.
In this study, the 200 outpatients were randomly assigned to either the St. John’s wort group or the placebo group. This randomness increases the likelihood that any differences in outcomes can be attributed to the treatment itself and not to pre-existing differences between the groups. Random assignment supports the validity of the study's conclusions.