Question

A study was conducted to determine whether the drug AZT was effective in preventing serious opportunistic infection among individuals infected with human immunodeficiency virus (HIV). Individuals who were HIV-positive were randomly selected to either receive AZT treatment or a placebo (Non drug) treatment. Among the 145 individuals who received AZT, 24 developed serious opportunistic infections. Among the 137 individuals who were not treated with AZT, 45 developed serious opportunistic infections.

Complete the 2x2 table for these data.

1. What type of study is this? How do you know? Be specific.

2. What is the measure of association for this study type?

3. Calculate the association between AZT treatment and the development of opportunistic infections.

Explain what this measure of association means.

Answer 1

ANSWER::

2*2 contingency table-

Corresponding 2*2 contingency table is as follows.

1.

This is an experimental study.

In an experimental study, researcher does not merely observe samples to collect data. Researcher divides available sample units randomly into treatment and control groups, provides item of interest to sample units of treatment group and placebo to sample units of control group, waits for some time (some days or months) to let the treatment affect sample units and finally collect data.

2.

For this study, two random variables (AZT treatment and development of opportunistic infections) are considered. Hence, Yule's coefficient of association is the perfect measure of association here.

3.

Yule's coefficient of association is given by

Hence, association between AZT treatment and the development of opportunistic infections is -0.4229714.

Measure of association indicates that there is a negative relation between AZT treatment and development of opportunistic infections. It suggests that on average, AZT treatment reduces development of opportunistic infections.

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