Chapter 11.3, Problem 33E

(a)

To determine

To explain: the researcher’s conclusion may not be valid.

Answer to Problem 33E

Here, the researcher did not take into account the previous heart conditions of the people he surveyed.

Explanation of Solution

Given:

175 people take fiber supplements

175 people do not take fiber supplements.

19.6% fewer heart attacks who took the supplements.

Calculation:

The researcher’s conclusion may not be valid because while conducting the survey. He did not take into account the previous heart conditions of the people he surveyed. And the chance of having heart attack is more for those people who have history of heart problem. Thus, the sample might not present the population correctly.

Conclusion:

Hence, here, the researcher did not take into account the previous heart conditions of the people he surveyed.

(b)

To determine

To describe: how the study should be conducted

Answer to Problem 33E

Here, to produce valid results, the researcher should have divided the population into groups based on the previous heart conditions and whether they take fiber supplements and then select a random sample from each other.

Explanation of Solution

Calculation:

To produce valid results, the researcher should have divided the population into groups based on the previous heart conditions and whether they take fiber supplements. And then select a random sample from each other.

By doing so, a sample can be obtained which accurately represent the populations.

Conclusion:

Hence, to produce valid results, the researcher should have divided the population into groups based on the previous heart conditions and whether they take fiber supplements and then select a random sample from each other.