A union spokesperson claims that 75% of union members will support a strike if their basic demands are not met. A company negotiator believes the true percentage is lower and runs a hypothesis test. What is the conclusion if 87 out of a simple random sample of 125 union members say they will strike?For each of the two possible answers above, what error might have been committed, Type I or Type II, and what would be a possible consequence?
Question
A union spokesperson claims that 75% of union members will support a strike if their basic demands are not met. A company negotiator believes the true percentage is lower and runs a hypothesis test. What is the conclusion if 87 out of a simple random sample of 125 union members say they will strike?For each of the two possible answers above, what error might have been committed, Type I or Type II, and what would be a possible consequence?
Solution
First, we need to set up our null and alternative hypotheses. The null hypothesis (H0) is that the true proportion of union members who will support a strike is 75% (0.75). The alternative hypothesis (H1) is that the true proportion is less than 75%.
Next, we calculate the sample proportion (p̂) which is 87/125 = 0.696.
Now, we need to perform a hypothesis test to determine if we should reject the null hypothesis in favor of the alternative hypothesis. We can use a one-sample z-test for proportions.
The test statistic (z) is calculated as follows:
z = (p̂ - p0) / sqrt[(p0 * (1 - p0)) / n]
where p0 is the proportion under the null hypothesis, n is the sample size, and sqrt is the square root function.
Substituting the given values:
z = (0.696 - 0.75) / sqrt[(0.75 * (1 - 0.75)) / 125] = -1.44
We compare this test statistic to a critical value from the standard normal distribution, typically -1.645 for a one-tailed test at the 5% significance level. Since -1.44 > -1.645, we do not reject the null hypothesis. This means that the company negotiator does not have enough evidence to support his claim that the true percentage is lower than 75%.
If we made a mistake by not rejecting the null hypothesis when it is false, we have committed a Type II error. The consequence of this error is that the company might underestimate the support for a strike among union members, potentially leading to a strike that they were not adequately prepared for.
If we rejected the null hypothesis when it is true, we would have committed a Type I error. The consequence of this error is that the company might overestimate the support for a strike, potentially leading to unnecessary concessions to the union.
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