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A chemical manufacturing company wants to locate a hazardous waste disposal site near a city of 50,000 residents and has offered substantial financial inducements to the city. Two hundred adults ( 110 women and 90 men) who are residents of this city are chosen at random. Sixty percent of these adults oppose the site, \(32 \%\) are in favor, and \(8 \%\) are undecided. Of those who oppose the site, \(65 \%\) are women; of those in favor, \(62.5 \%\) are men. Using a \(5 \%\) level of significance, can you conclude that opinions on the disposal site are dependent on gender?

Short Answer

Expert verified
The conclusion whether opinions on the disposal site are dependent on gender can only be drawn after performing the chi-square test of independence on the observed data and comparing the test statistic value with the critical value at a 5% level of significance.

Step by step solution

01

Formulating Hypotheses

Our null hypothesis will be that the opinions on the disposal site are independent of gender. The alternative hypothesis states that the opinions on the disposal site are dependent on gender. So, \(H_0: \) Opinions and gender are independent. \(H_1: \) Opinions and gender are dependent.
02

Constructing Contingency Table and Calculating Expected Frequencies

A contingency table is to be constructed, with the rows representing the different opinions (oppose, favor, undecided) and the columns representing the different genders (men, women). The cells of the table will include both observed frequencies and expected frequencies computed using the formula \(\frac{(row total * column total)}{sample size}\).
03

Calculating Chi-Square Statistic

Next, the chi-square statistic is calculated, using the formula: \(\chi^2 = \Sigma \frac{(Observed-Expected)^2}{Expected}\)For each cell to be computed and summed to give a total chi-square statistic value.
04

Comparison to Critical Value

The critical value for the chi-square statistic at \(5\%\) level of significance with appropriate degrees of freedom (df) can be extracted from a Chi-square distribution table. Then, compare the calculated Chi-square test statistic value with the critical value.
05

Making Decision

Lastly, based on the comparison result from the previous step, if the calculated Chi-square statistic is greater than the critical value, reject the null hypothesis and conclude that the opinions on the disposal site are dependent on gender. If not, fail to reject the null hypothesis and conclude that the opinions and gender are independent.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Contingency Table
In statistical analysis, a contingency table is a handy tool used to organize data by categories to find the relationship between variables. It's especially useful in hypothesis testing. For the given problem, the table consists of rows and columns. Each row represents the different opinions about the hazardous waste site: oppose, favor, and undecided. Similarly, each column represents a category of gender: men and women.

The cells inside the table hold both observed frequencies from the sample and the expected frequencies. The expected frequencies are computed using the formula: \(\text{Expected frequency} = \frac{\text{Row total} \times \text{Column total}}{\text{Total sample size}}\).

By systematically organizing this data, a contingency table allows us to easily perform further statistical tests, such as the Chi-Square test, to investigate the relationships between gender and opinions on the disposal site.
Hypothesis Testing
Hypothesis testing is a crucial process in statistics that allows us to make informed conclusions based on sample data. In this exercise, we begin by formulating two main hypotheses:

  • **Null Hypothesis (\(H_0\)):** Gender and opinions are independent. This means that opinions on the waste site are not influenced by whether the person is a man or a woman.
  • **Alternative Hypothesis (\(H_1\)):** Gender and opinions are dependent. This suggests that opinions may vary significantly across genders.

The goal is to analyze the data collected in the contingency table and use the Chi-Square test to determine whether to accept or reject the null hypothesis. Hypothesis testing follows a standard process:

1. Setting up the hypotheses
2. Conducting statistical tests
3. Deciding based on results

This systematic approach helps ensure that the decisions made are backed by empirical data rather than mere speculation.
Gender and Opinion Independence
The concept of independence in statistical terms refers to whether the occurrence or variation of one variable is unaffected by the occurrence of another. In this context, we are curious about whether opinions on the hazardous waste site depend on the gender of the individuals.

If our final analysis shows that gender and opinion are independent, it means there's no statistical evidence that men and women feel differently about the waste site. On the other hand, if they're found to be dependent, it implies that opinions are somehow linked with gender.

Understanding this relationship is critical for decision-makers who need to be aware of public opinion and potential biases by demographics. It helps ensure that the financial inducements offered are fair and aligned with community concerns or support.
Critical Value
The critical value is a crucial threshold in hypothesis testing that helps us make a decision about the null hypothesis. It represents the point beyond which we would consider the outcome statistically significant.

In the context of the Chi-Square test, the critical value is determined based on the level of significance, often denoted by \(\alpha\), and the degrees of freedom in the data. For this exercise, we are working with a \(5\%\) level of significance, which implies we're looking for enough evidence to be 95% confident that any observed relationship is not due to random chance.

The degrees of freedom, meanwhile, depend on the number of categories minus one for each dimension (rows and columns) in our contingency table: \(\text{(Number of rows - 1)} \times \text{(Number of columns - 1)}\). Using these two factors, the critical value can be extracted from a Chi-square distribution table.

If the calculated Chi-square statistic exceeds this critical value, it means the likelihood of the observed data occurring under the null hypothesis is very low, leading us to reject \(H_0\) in favor of \(H_1\).

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Most popular questions from this chapter

To make a test of independence or homogeneity, what should be the minimum expected frequency for each cell? What are the alternatives if this condition is not satisfied?

Two random samples, one of 95 blue-collar workers and a second of 50 white- collar workers, were taken from a large company. These workers were asked about their views on a certain company issue. The following table gives the results of the survey. $$ \begin{array}{lccc} \hline & \multicolumn{3}{c} {\text { Opinion }} \\ \cline { 2 - 4 } & \text { Favor } & \text { Oppose } & \text { Uncertain } \\\ \hline \text { Blue-collar workers } & 44 & 39 & 12 \\ \text { White-collar workers } & 21 & 26 & 3 \\ \hline \end{array} $$ Using a \(2.5 \%\) significance level, test the null hypothesis that the distributions of opinions are homogeneous for the two groups of workers.

Of all students enrolled at a large undergraduate university, \(19 \%\) are seniors, \(23 \%\) are juniors, \(27 \%\) are sophomores, and \(31 \%\) are freshmen. A sample of 200 students taken from this university by the student senate to conduct a survey includes 50 seniors, 46 juniors, 55 sophomores, and 49 freshmen. Using a \(2.5 \%\) significance level, test the null hypothesis that this sample is a random sample.

Explain the difference between the observed and expected frequencies for a goodness-of-fit test.

According to a Gallup poll whose results were reported on October 22, 2013, American's views on legalizing marijuana are changing. In that survey, American adults were asked whether marijuana should be legalized in America. Suppose in a recent survey, 600 Americans were randomly selected from each of the four age groups listed in the table below. The frequencies of the responses for various age groups are listed in this table assuming that every person included in the survey responded yes or no. $$ \begin{array}{lll} \hline & \text { Yes } & \text { No } \\ \hline 18 \text { to } 29 & 402 & 198 \\ 30 \text { to } 49 & 372 & 228 \\ 50 \text { to } 64 & 336 & 264 \\ 65+ & 270 & 330 \\ \hline \end{array} $$ Test at a \(1 \%\) significance level whether the proportion of Americans who support legalizing marijuana is the same for each of the age groups.

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