Elementary Statistics – Experiment Examples

 

  1. State whether each scenario below is an example of an observational study or an experiment. Furthermore, identify the explanatory variable and the response variable.

 

·         A researcher is interested in the whether drug use during pregnancy affects the baby’s birth weight. He takes a sample of 20 pregnant women who are drug users and 20 who are not. He follows their pregnancies and compares the birth weights of the babies between the two groups.

 

 

 

·         A researcher is interested in whether exercise affects quality of sleep. He finds 50 volunteers who do not exercise regularly, and he asks them to rate the quality of their sleep. Then he puts 25 of the volunteers on an exercise program for 3 months, while the other 25 do not exercise. After 3 months he asks the volunteers to again rate their quality of sleep. Then he compares the differences in the two groups.

 

 

 

 

  1. A researcher is interested in the effect of vitamin C and exercise on the common cold. She finds 24 volunteers to participate in her study. Subjects either take vitamin C or a placebo and either partake in an exercise program or do not partake. At the end of 6 months, the researcher will record the number of times each volunteer got a cold, and she will compare between the groups.

 

    1. What are the factors, and what are the levels of the factors? How many total treatments are there?

 

 

 

    1. What is the response variable?

 

 

 

    1. Blinding, and perhaps double blinding, should be used in this experiment. Why?

 

 

 

    1. Carefully draw (and label) a diagram depicting a completely randomized design for this experiment.

      2.
    2. The list of the volunteers is shown below:

Susie                        Bob

Karen                      Joe          

Kathy                      Peter       

Jane                         John

Jill                            Jack

Myrtle                     Jason      

Sally                         Lloyd

Emily                      Bruce

Diane                      Richard

Beth                        Bill

Carol                       Bubba

Liz                           Jim

 

What would happen if, rather than random assignment, we simply put the first 6 people in the first group, the second 6 in the second group, etc.?

 

 

 

 

    1. Carry out the randomization for Group 1 starting at line 184 of Table B. (The other groups are determined in an analogous way.)

 

 

 

 

 

 

 

 

 

 

    1. Now suppose the researcher is solely interested in the effect of vitamin C (not exercise). Furthermore, before the experiment is run, the researcher learns that men and women react very differently to vitamin C. She then decides to use a block design. Draw (and label) a diagram depicting the block design. Furthermore, discuss how the randomization would be done for this block design.