Five Steps of Hypothesis Testing
Week3 Practice Worksheet
Five Steps of Hypothesis Testing
6. A psychology professor of a large class became curious as to whether the students who turned in tests first scored differently from the overall mean on the test. The overall mean score on the test was 75 with a standard deviation of 10; the scores were approximately normally distributed. The mean score for the first 20 students to turn in tests was 78. Using the .05 significance level, was the average test score earned by the first 20 students to turn in their tests significantly different from the overall mean?
a. Use the five steps of hypothesis testing.
b. Figure the confidence limits for the 95% confidence interval.
References
Five Step Hypothesis Testing Procedure
The examples on the following pages use the five step hypothesis testing procedure outlined below. This is the same procedure that we used to conduct a hypothesis test for a single mean, single proportion, difference in two means, and difference in two proportions.
When conducting a chi-square goodness-of-fit test, it makes the most sense to write the hypotheses first. The hypotheses will depend on the research question. The null hypothesis will always contain the equalities and the alternative hypothesis will be that at least one population proportion is not as specified in the null.
In order to use the chi-square distribution to approximate the sampling distribution, all expected counts must be at least five.
- Expected Count
Where
is the total sample size and
- is the hypothesized population proportion in the “ith” group.
To check this assumption, compute all expected counts and confirm that each is at least five.
In Step 1 you already computed the expected counts. Use this formula to compute the chi-square test statistic:
- Chi-Square Test Statistic
Where is the observed count for each cell and
- is the expected count for each cell.
Construct a chi-square distribution with degrees of freedom equal to the number of groups minus one. The p-value is the area under that distribution to the right of the test statistic that was computed in Step 2. You can find this area by constructing a probability distribution plot in Minitab Express.
Unless otherwise stated, use the standard 0.05 alpha level.
reject the null hypothesis.
fail to reject the null hypothesis.
Go back to the original research question and address it directly. If you rejected the null hypothesis, then there is evidence that at least one of the population proportions is not as stated in the null hypothesis. If you failed to reject the null hypothesis, then there is not evidence that any of the population proportions are different from what is stated in the null hypothesis.
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