Age at First Marriage A marriage counselor claims that the median age of men at the time of their first marriage is greater than 28 years old. In a random sample of 56 men, 33 were less than 28 years old and 23 were more than 28 years old at the time of their first marriage. At α = 0.05, can you support the counselor’s claim? (Adapted from U.S. Census Bureau)
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 53m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 12m
- 9. Hypothesis Testing for One Sample2h 19m
- 10. Hypothesis Testing for Two Samples3h 22m
- 11. Correlation1h 6m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 20m
- 14. ANOVA1h 0m
9. Hypothesis Testing for One Sample
Steps in Hypothesis Testing
Problem 11.1.13a
Textbook Question
Performing a Sign Test In Exercises 7–22, (a) identify the claim and state Ho and Ha,
Social Media A research group claims that the median age of the users of a social media website is greater than 30 years old. In a random sample of 24 users, 11 are less than 30 years old, 10 are more than 30 years old, and 3 are 30 years old. At , can you support the research group’s claim? (Adapted from Pew Research Center)

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Step 1: Identify the claim and hypotheses. The claim is that the median age of the users of the social media website is greater than 30 years old. This translates to the alternative hypothesis (Ha): the median age > 30. The null hypothesis (Ho) is the opposite: the median age ≤ 30.
Step 2: Exclude the data points that are exactly equal to the median (30 years old). In this case, there are 3 users with an age of 30, so they are excluded. This leaves 11 users with ages less than 30 and 10 users with ages greater than 30.
Step 3: Perform the sign test. Assign a '+' sign to the data points greater than 30 and a '-' sign to the data points less than 30. Count the number of '+' signs (10) and '-' signs (11). The test statistic is the smaller of these two counts, which is 10.
Step 4: Determine the critical value. Use the binomial distribution with n = 21 (the total number of data points after excluding the median) and p = 0.5 (assuming the null hypothesis is true). Find the critical value for the given significance level (α).
Step 5: Compare the test statistic to the critical value. If the test statistic is less than or equal to the critical value, fail to reject the null hypothesis. Otherwise, reject the null hypothesis and conclude that there is sufficient evidence to support the claim that the median age is greater than 30 years old.

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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 two competing hypotheses: the null hypothesis (H0), which represents a statement of no effect or no difference, and the alternative hypothesis (Ha), which represents the claim being tested. In this case, H0 would state that the median age is less than or equal to 30, while Ha would assert that the median age is greater than 30.
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Step 1: Write Hypotheses
Sign Test
The Sign Test is a non-parametric statistical test used to determine if there is a significant difference between the median of a sample and a specified value. It is particularly useful when the data does not meet the assumptions required for parametric tests. In this scenario, the Sign Test will help assess whether the number of users below and above the median age of 30 supports the research group's claim.
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Independence Test
P-value
The P-value is a measure that helps determine the strength of the evidence against the null hypothesis. It represents the probability of observing the sample data, or something more extreme, if the null hypothesis is true. A small P-value (typically less than 0.05) indicates strong evidence against H0, suggesting that the alternative hypothesis may be true. In this exercise, calculating the P-value will help decide whether to reject H0 in favor of Ha.
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Step 3: Get P-Value
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