Math Problem Statement

Among drivers who have had a car crash in the last year, 300 were randomly selected and categorized by age, with the results listed in the table below. Age Under 25 25-44 45-64 Over 64 Drivers 116 70 46 68 If all ages have the same crash rate, we would expect (because of the age distribution of licensed drivers) the given categories to have 16%, 44%, 27%, 13% of the subjects, respectively. At the 0.025 significance level, test the claim that the distribution of crashes conforms to the distribution of ages. The test statistic is

The critical value is

The conclusion is A. There is not sufficient evidence to warrant the rejection of the claim that the distribution of crashes conforms to the distibuion of ages. B. There is sufficient evidence to warrant the rejection of the claim that the distribution of crashes conforms to the distibuion of ages.

Solution

This is a Chi-Square Goodness-of-Fit Test problem to determine if the observed crash distribution matches the expected distribution of crashes based on the age distribution.

Steps to Solve:

  1. State the Null and Alternative Hypotheses:

    • H0H_0: The observed crash distribution conforms to the expected age distribution.
    • HaH_a: The observed crash distribution does not conform to the expected age distribution.
  2. Calculate the Expected Frequencies: Multiply the total number of drivers (300) by the expected percentages for each age group:

    • Under 25: 300×0.16=48300 \times 0.16 = 48
    • 25-44: 300×0.44=132300 \times 0.44 = 132
    • 45-64: 300×0.27=81300 \times 0.27 = 81
    • Over 64: 300×0.13=39300 \times 0.13 = 39
  3. Compute the Test Statistic: The test statistic for a Chi-Square Goodness-of-Fit test is: χ2=(OE)2E\chi^2 = \sum \frac{(O - E)^2}{E} where OO is the observed frequency, and EE is the expected frequency. Calculate for each group:

    • Under 25: (11648)248=68248=96.17\frac{(116 - 48)^2}{48} = \frac{68^2}{48} = 96.17
    • 25-44: (70132)2132=(62)2132=29.12\frac{(70 - 132)^2}{132} = \frac{(-62)^2}{132} = 29.12
    • 45-64: (4681)281=(35)281=15.12\frac{(46 - 81)^2}{81} = \frac{(-35)^2}{81} = 15.12
    • Over 64: (6839)239=29239=21.56\frac{(68 - 39)^2}{39} = \frac{29^2}{39} = 21.56

    Sum these values to find χ2\chi^2: χ2=96.17+29.12+15.12+21.56=161.97\chi^2 = 96.17 + 29.12 + 15.12 + 21.56 = 161.97

  4. Find the Critical Value: Degrees of freedom (df) = Number of categories - 1 = 4 - 1 = 3. At a significance level of 0.025, the critical value from the Chi-Square table is approximately 11.34511.345.

  5. Make a Decision:

    • If χ2>critical value\chi^2 > \text{critical value}, reject H0H_0.
    • Here, 161.97>11.345161.97 > 11.345, so we reject H0H_0.

Conclusion:

  • The conclusion is B: There is sufficient evidence to warrant the rejection of the claim that the distribution of crashes conforms to the distribution of ages.

Do you want further clarification or a breakdown of the calculations? Here are 5 related questions:

  1. How is the Chi-Square test used in hypothesis testing?
  2. Can you explain why degrees of freedom matter in this test?
  3. How do we interpret the critical value in a Chi-Square test?
  4. What other scenarios would use a Chi-Square Goodness-of-Fit Test?
  5. How does significance level affect the test result?

Tip:

Always check if the expected frequencies are all greater than 5. If not, the Chi-Square test may not be valid, and you might need to combine categories or use a different test.

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Math Problem Analysis

Mathematical Concepts

Chi-Square Goodness-of-Fit Test
Hypothesis Testing
Probability Distribution

Formulas

Chi-Square Test Statistic: χ² = Σ((O - E)² / E)
Expected Frequency Calculation: E = Total × Proportion

Theorems

Chi-Square Distribution Theorem

Suitable Grade Level

Grades 11-12 or College Level