Question

Researchers want to compare the effectiveness of an extract of St. John's Wort with placebo in outpatients with major depression. 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 extrat, 900 milligrams per day (mg/day) for 4 weeks, increased to 1200 mg/day 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 data, it was concluded that St. John's Wort was not effective for treatment of major depression.

Required:
a. What type of experimental design this is?
b. What is the population that is being studied?
c. What is the response variable in this study?
d. What are the treatments?
e. Identify the experimental units.
f. What is the control group in this study?

Answer 1

a) Experimental Design: Randomised Experimental Design

b) Population : All Adult outpatients diagnosed with major depression

c) Responsive Variable : Effectiveness of extracts on depression patients' HAM-D rating

d) Treatments : John Wart extracts or Placebo

e) Experimental units : 200 adult outpatients diagnosed with major depression having HAM-D score > 20

Explanation:

a) Randomised Experimental Design is being used : As experimental units are randomly assigned to any of the experimental groups, each receiving different treatments

b) Population refers to the entire group of objects or individuals, to whom the experiment research can be applied. So, all adult outpatients diagnosed with major depression as per HAM-D depression score are population

c) Responsive variable is the dependent variable being affected by independent variables. It is effectiveness of extracts on depression patients, ie change in change on the HAM-D depression rating

d) Treatments are the ways or objects with which experimental units are treated. These are John wart extracts or Placebo

e) Experimental units are the selected sample people or objects for experiment conduct. These are '200' adult outpatients diagnosed with major depression, having a baseline Hamilton Rating Scale for Depression (HAM-D) score > 20