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Chi-square Goodness of Fit test

Consider the following problem:
A research firm claims that the distribution of the days of the week that people are most likely to order food for delivery is different from the distribution seen in the past. You randomly select 494 people and record which day of the week each is most likely to order food for delivery. The table below also shows the results of your count. At alpha, α, = 0.05, test the research firm’s claim.

This sounds like a test of Goodness of Fit between the historical pattern and the observed pattern.

The claim is that the actual pattern and the historical pattern are different. That means we need the inequality math operator, which, in turn, means the claim is the alternative hypothesis.

Stating our two hypotheses:Chi-square Goodness of Fit test

Example problem re: Goodness of Fit test:

You are given a six-faced die and asked to determine with 95% confidence if it is “fair.”

  • What are the hypotheses?

Answer: the null H0: the die is fair, p1 = p2 = … = p6 = 1/6; the alternative Ha: the die is not fair, at least one pi ≠ 1/6.

  • What is the critical value of chi-square?

Answer: degrees of freedom df = 6 – 1 = 5. From a table or calculator, χ0.052 =11.071.

Common student mistake #1:Example problem re: Goodness of Fit test: