Question

Many people start their day with a jolt of caffeine from coffee or a soft drink. Most experts agree that people who consume large amounts of caffeine each day may suffer from physical withdrawal symptoms if they stop ingesting their usual amounts of caffeine. Researchers recruited $11$volunteers who were caffeine dependent and who were willing to take part in a caffeine withdrawal experiment. The experiment was conducted on two 2-day periods that occurred one week apart. During one of the 2-day periods, each subject was given a capsule containing the amount of caffeine normally ingested by that subject in one day. During the other study period, the subjects were

given placebos. The order in which each subject received the two types of capsules was randomized. The subjects’ diets were restricted during each of the study periods. At the end of each 2-day study period, subjects were evaluated using a tapping task in which they were instructed to press a button $200$times as fast as they could.

a. Identify the explanatory and response variables in this experiment.

b. How was blocking used in the design of this experiment? What is the benefit of blocking in this context?

c. Researchers randomized the order of the treatments to avoid confounding. Explain how confounding might occur if the researchers gave all subjects the placebo first and the caffeine second. In this context, what problem does confounding cause?

d. Could this experiment have been carried out in a double-blind manner? Explain your answer.

Short answer

a) The results to be compared are the differences between the caffeine and the placebo scores on the tapping test.

b) The order was randomised to control for any possible influence of the order in which the treatments were administered on the subject’s tapping speed.

c) The subjects nor the people who come in contact with them during the experiment

d) This experiment can be conducted in a double-blind fashion

Step-by-step solution

Part (a) Step 1: Given information

We have to Identify the explanatory and response variables in this experiment.

Part (a) Step 2: Explanation

In a matched pairs configuration, each of the 11 people represented a block. On one of the two days, each subject received caffeine tablets and on the other, a placebo. The caffeine or placebo was given to them in a random order. The tapping test was administered at the end of the 2-day trial. The results to be compared are the differences between the caffeine and the placebo scores on the tapping test. Individual differences in dexterity were taken into account through blocking.

Part (b) Step 1: Given information

We have to tell how was blocking used in the design of this experiment? What is the benefit of

blocking in this context.

Part (b) Step 2: Explanation

The order was randomised to control for any possible influence of the order in which the treatments were administered on the subject’s tapping speed.

Part (c) Step 1: Given information

We have to explain how confounding might occur if the researchers gave all subjects.

Part (c) Step 2: Explanation

This experiment can be carried out under double-blind conditions. This means that neither the subjects nor others who interact with them during the experiment (such as those who count the number of taps) are aware of the order in which the caffeine or placebo was given.

Part (c) Step 1: Given information

We have to tell could this experiment have been carried out in a double-blind manner

Part (d) Step 2: Explanation

This experiment can be carried out under double-blind conditions. This means that neither the subjects nor anyone who come into contact with them during the experiment (such as those who count the taps) are aware of the order in which the caffeine or placebo was given.