Table of contents
- 1. Intro to Stats and Collecting Data55m
- 2. Describing Data with Tables and Graphs1h 55m
- 3. Describing Data Numerically1h 45m
- 4. Probability2h 16m
- 5. Binomial Distribution & Discrete Random Variables2h 33m
- 6. Normal Distribution and Continuous Random Variables1h 38m
- 7. Sampling Distributions & Confidence Intervals: Mean1h 3m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 12m
- 9. Hypothesis Testing for One Sample1h 1m
- 10. Hypothesis Testing for Two Samples2h 8m
- 11. Correlation48m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 20m
- 14. ANOVA1h 0m
13. Chi-Square Tests & Goodness of Fit
Goodness of Fit Test
Problem 11.RE.1
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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Step 1: Identify the hypothesis. The null hypothesis (Hâ‚€) states that weather-related deaths occur with the same frequency across all months. The alternative hypothesis (Hâ‚) states that weather-related deaths do not occur with the same frequency across all months.
Step 2: Choose the appropriate test. Since we are comparing observed frequencies (the number of deaths in each month) to expected frequencies (assuming equal distribution), we use the chi-square goodness-of-fit test.
Step 3: Calculate the expected frequency for each month. Assuming equal distribution, divide the total number of deaths by the number of months. Use the formula: Expected frequency = Total deaths / 12.
Step 4: Compute the chi-square test statistic. Use the formula: χ² = Σ((Oᵢ - Eᵢ)² / Eᵢ), where Oᵢ is the observed frequency for each month, and Eᵢ is the expected frequency. Perform this calculation for all 12 months and sum the results.
Step 5: Compare the test statistic to the critical value. Determine the degrees of freedom (df = number of categories - 1 = 12 - 1 = 11) and find the critical value for a 0.01 significance level from the chi-square distribution table. If the test statistic exceeds the critical value, reject the null hypothesis; otherwise, fail to reject it.

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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 or difference. In this context, the null hypothesis would state that weather-related deaths occur with the same frequency across all months, while the alternative would suggest that they do not.
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Step 1: Write Hypotheses
Chi-Square Test
The Chi-Square test is a statistical test used to determine if there is a significant association between categorical variables. In this scenario, it can be applied to assess whether the observed frequencies of weather-related deaths in each month differ significantly from the expected frequencies if deaths were uniformly distributed. The test calculates a Chi-Square statistic, which is then compared to a critical value from the Chi-Square distribution to determine significance.
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Step 2: Calculate Test Statistic
Significance Level
The significance level, often denoted as alpha (α), is the threshold for determining whether to reject the null hypothesis. In this case, a significance level of 0.01 indicates that there is a 1% risk of concluding that a difference exists when there is none. If the p-value obtained from the Chi-Square test is less than 0.01, it suggests that the differences in weather-related deaths across months are statistically significant, warranting further investigation.
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Step 4: State Conclusion Example 4
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