Question

A researcher is interested in studying the effect of iron on human memory so he comes up with the following plan for an experiment. The experiment will involve 100 volunteers where 50 volunteers are randomly selected from all female volunteers and 50 are randomly selected from all male volunteers. Each volunteer will take a memory test 30 minutes after eating spinach. Some volunteers will be randomly assigned to eat iron-free spinach; some will eat regular spinach (with iron); others will eat a mixture of the two which contains only half the amount of iron. For each volunteer, a test score (the number of items recalled correctly) will be recorded. The volunteers will not be told which type of spinach they have been given, but the researcher who evaluates the results will prepare the cans of spinach right on the spot (out of sight of the volunteers).

Part i) What sampling technique is used to obtain the 100 volunteers to participate in the study?

A. Stratified random sampling
B. One-stage cluster sampling
C. Two-stage cluster sampling
D. Simple random sampling
E. Systematic sampling


Part ii) Which of the following features is/are present in this study? CHECK ALL THAT APPLY.

A. Double blinding
B. Blocking
C. Single blinding
D. Replication
E. Confounding
F. None of the above


Part iii) The treatments of this study is/are:

A. a can of spinach
B. no iron, half dose of iron and full dose of iron
C. iron-free spinach and regular spinach with iron
D. iron

The study finds that the group of volunteers who eat regular spinach has a significantly higher average test score than the group who eat iron-free spinach. This implies:

A. The difference in the average test score between the regular spinach group and the iron-free spinach group is so large that it can be explained by chance.
B. The difference in the average test score between the regular spinach group and the iron-free spinach group is so large that it cannot be explained by chance.
C. The difference in the average test score between the regular spinach group and the iron-free spinach group is so small that it cannot be explained by chance.
D. The difference in the average test score between the regular spinach group and the iron-free spinach group is so small that it can be explained by chance.

Answer 1

Part i) A. Stratified Random Sampling.

Here male volunteers and female volunteers are the two strata of the population of volunteers and random sample of size 50 is drawn from each strata.

Part ii) C. Single blinding. Because the volunteers do not know what type of spinach they are getting, where as the researcher knows which volunteer is getting which type of spinach.

D. Replication. Each spinach type is given to several randomly selected volunteers who took the memory test.

Part iii)

B. no iron, half dose of iron and full dose of iron

B. The difference in the average test score between the regular spinach group and the iron-free spinach group is so large that it cannot be explained by chance.