Chi square test for cola preference

Can people really identify their favorite brand of cola? Volunteers tasted Coca-Cola Classic, Pepsi, Diet Coke, and Diet Pepsi, with the results shown below. Research question: At alpha = .05, is the correctness of the prediction different for the two types of cola drinkers? Could you identify your favorite brand in this kind of test? Since it is a 2 × 2 table, try also a two-tailed two-sample z test for pi1 = pi2 (see Chapter 10) and verify that z2 is the same as your chi-square statistic. Which test do you prefer? Why? (Data are from Consumer Reports 56, no. 8 [August 1991], p. 519.) Cola

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Answer
The null hypothesis tested is
H0: The vehicle type does not vary by mall location.
H1: The vehicle type varies by mall location.
The test Statistic used is where O is the observed frequency and E is the expected frequency.
Rejection Criteria: Reject the null hypothesis, if the calculated value of chi square is greater than the critical value of Chi square with 12 d.f at 0.05 significance level.
The expected frequencies are given ...