Math Problem Statement

Given the 4 categories and distribution, apply the Goodness-of-fit test for the claim that the 4 categories occur with the following distribution: H0: pA = 0.15, pB = 0.4, pC = 0.3, pD = 0.15. Observed frequencies: A = 19, B = 57, C = 46, D = 12. Complete the table for the expected frequencies, find the chi-square test statistic, p-value, and determine if you reject or fail to reject the null hypothesis at a 0.025 significance level.

Solution

To solve the problem presented in the image, we need to follow these steps:

  1. Calculate the Expected Frequencies:

    • The expected frequency for each category is calculated using the formula: Ei=npiE_i = n \cdot p_i where nn is the total number of observations and pip_i is the proportion for each category.

    The total number of observations (nn) is: n=19+57+46+12=134n = 19 + 57 + 46 + 12 = 134

    Using the given proportions pA=0.15p_A = 0.15, pB=0.4p_B = 0.4, pC=0.3p_C = 0.3, pD=0.15p_D = 0.15, we calculate:

    EA=1340.15=20.1E_A = 134 \cdot 0.15 = 20.1 EB=1340.4=53.6E_B = 134 \cdot 0.4 = 53.6 EC=1340.3=40.2E_C = 134 \cdot 0.3 = 40.2 ED=1340.15=20.1E_D = 134 \cdot 0.15 = 20.1

  2. Compute the Chi-Square Test Statistic:

    • The Chi-Square test statistic is calculated using the formula: χ2=(OiEi)2Ei\chi^2 = \sum \frac{(O_i - E_i)^2}{E_i} where OiO_i is the observed frequency and EiE_i is the expected frequency.

    For each category: χA2=(1920.1)220.1=1.2120.1=0.0602\chi^2_A = \frac{(19 - 20.1)^2}{20.1} = \frac{1.21}{20.1} = 0.0602 χB2=(5753.6)253.6=11.5653.6=0.2157\chi^2_B = \frac{(57 - 53.6)^2}{53.6} = \frac{11.56}{53.6} = 0.2157 χC2=(4640.2)240.2=33.6440.2=0.8366\chi^2_C = \frac{(46 - 40.2)^2}{40.2} = \frac{33.64}{40.2} = 0.8366 χD2=(1220.1)220.1=65.6120.1=3.2632\chi^2_D = \frac{(12 - 20.1)^2}{20.1} = \frac{65.61}{20.1} = 3.2632

    Summing these up: χ2=0.0602+0.2157+0.8366+3.2632=4.3757\chi^2 = 0.0602 + 0.2157 + 0.8366 + 3.2632 = 4.3757

    Rounded to three decimal places, χ24.376\chi^2 \approx 4.376.

  3. Determine the p-value:

    • To find the p-value, we use the Chi-Square distribution with df=k1df = k - 1 degrees of freedom, where kk is the number of categories. df=41=3df = 4 - 1 = 3

    Using

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Math Problem Analysis

Mathematical Concepts

Chi-Square Test
Goodness-of-Fit
Statistical Hypothesis Testing

Formulas

Expected Frequency: E_i = n * p_i
Chi-Square Test Statistic: χ² = Σ((O_i - E_i)² / E_i)

Theorems

Chi-Square Distribution
Null Hypothesis Significance Testing

Suitable Grade Level

Undergraduate Level - Introductory Statistics