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Ch. 11 - Goodness-of-Fit and Contingency Tables
Triola - Elementary Statistics 14th Edition
Triola14th EditionElementary StatisticsISBN: 9780137366446Not the one you use?Change textbook
Chapter 11, Problem 11.1.7

In Exercises 5–20, conduct the hypothesis test and provide the test statistic and the P-value and/or critical value, and state the conclusion.


Testing a Slot Machine The author purchased a slot machine (Bally Model 809) and tested it by playing it 1197 times. There are 10 different categories of outcomes, including no win, win jackpot, win with three bells, and so on. When testing the claim that the observed outcomes agree with the expected frequencies, the author obtained a test statistic of x2 = 8.815 Use a 0.05 significance level to test the claim that the actual outcomes agree with the expected frequencies. Does the slot machine appear to be functioning as expected?

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Step 1: Identify the type of hypothesis test to be conducted. This problem involves testing whether the observed frequencies agree with the expected frequencies, which is a Chi-Square Goodness-of-Fit test.
Step 2: State the null and alternative hypotheses. The null hypothesis (H₀) is that the observed outcomes agree with the expected frequencies. The alternative hypothesis (H₁) is that the observed outcomes do not agree with the expected frequencies.
Step 3: Determine the degrees of freedom (df) for the Chi-Square test. The formula for degrees of freedom is df = (number of categories - 1). Since there are 10 categories, df = 10 - 1 = 9.
Step 4: Find the critical value for the Chi-Square test at the 0.05 significance level with 9 degrees of freedom. Use a Chi-Square distribution table or software to locate the critical value.
Step 5: Compare the test statistic (χ² = 8.815) to the critical value and/or calculate the P-value. If the test statistic is less than the critical value or if the P-value is greater than 0.05, fail to reject the null hypothesis. Otherwise, reject the null hypothesis. Based on this comparison, state whether the slot machine appears to be functioning as expected.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hypothesis Testing

Hypothesis testing is a statistical method used to make decisions about a population based on sample data. It involves formulating a null hypothesis (H0) that represents no effect or no difference, and an alternative hypothesis (H1) that indicates the presence of an effect. The test statistic is calculated from the sample data, and this statistic is then compared to a critical value or used to find a P-value to determine whether to reject or fail to reject the null hypothesis.
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Step 1: Write Hypotheses

Chi-Squared Test

The Chi-squared test is a statistical test used to determine if there is a significant difference between the expected and observed frequencies in categorical data. In this context, it assesses whether the outcomes of the slot machine align with the expected distribution of outcomes. The test statistic, denoted as x², is calculated by summing the squared differences between observed and expected frequencies, divided by the expected frequencies, and is compared against a Chi-squared distribution to evaluate significance.
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Step 2: Calculate Test Statistic

Significance Level

The significance level, often denoted as alpha (α), is the threshold used to determine whether to reject the null hypothesis in hypothesis testing. A common significance level is 0.05, which indicates a 5% risk of concluding that a difference exists when there is none (Type I error). In this scenario, if the P-value obtained from the Chi-squared test is less than 0.05, it suggests that the observed outcomes significantly differ from the expected frequencies, leading to a rejection of the null hypothesis.
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Step 4: State Conclusion Example 4
Related Practice
Textbook Question

Questions 6–10 refer to the sample data in the following table, which describes the fate of the passengers and crew aboard the Titanic when it sank on April 15, 1912. Assume that the data are a sample from a large population and we want to use a 0.05 significance level to test the claim that surviving is independent of whether the person is a man, woman, boy, or girl.



Given that the P-value for the hypothesis test is 0.000 when rounded to three decimal places, what do you conclude? What do the results indicate about the rule that women and children should be the first to be saved?

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Textbook Question

In Exercises 5–20, conduct the hypothesis test and provide the test statistic and the P-value and/or critical value, and state the conclusion.


Heights Measured or Reported? Repeat the preceding exercise using the frequencies in the following table, which summarizes all of the 2784 male heights listed in Data Set 4 “Measured and Reported.” Does the larger data set have much of an effect on the results from Exercise 5?

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Textbook Question

In Exercises 5–20, conduct the hypothesis test and provide the test statistic and the P-value and/or critical value, and state the conclusion.


Bias in Clinical Trials? Researchers investigated the issue of race and equality of access to clinical trials. The following table shows the population distribution and the numbers of participants in clinical trials involving lung cancer (based on data from “Participation in Cancer Clinical Trials,” by Murthy, Krumholz, and Gross, Journal of the American Medical Association, Vol. 291, No. 22). Use a 0.01 significance level to test the claim that the distribution of clinical trial participants fits well with the population distribution. Is there a race/ethnic group that appears to be very underrepresented?


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Textbook Question

Identifying Hypotheses Refer to the data given in Exercise 1 and assume that the requirements are all satisfied and we want to conduct a hypothesis test of independence using the methods of this section. Identify the null and alternative hypotheses.

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Textbook Question

Does the Treatment Affect Success? The following table lists frequencies of successes and failures for different treatments used for a stress fracture in a foot bone (based on data from “Surgery Unfounded for Tarsal Navicular Stress Fracture,” by Bruce Jancin, Internal Medicine News, Vol. 42, No. 14). Use a 0.05 significance level to test the claim that success of the treatment is independent of the type of treatment. What does the result indicate about the increasing trend to use surgery?



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Textbook Question

Weather-Related Deaths For the most recent year as of this writing, the numbers of weather-related U.S. deaths for each month were 61, 14, 22, 26, 29, 42, 93, 49, 47, 35, 96, 16, listed in order beginning with January (based on data from the National Weather Service). Use a 0.01 significance level to test the claim that weather-related deaths occur in the different months with the same frequency. Provide an explanation for the result.

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