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.

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