The owner of a laboratory wants to keep sick leave as low as possible by keeping employees healthy through disease prevention programs.

• Group 1:Not provided with the vaccine (unvaccinated control group, N = 84)
• Group 2:Provided with the vaccine (vaccinated experimental group, N = 84)

In this case, the independent variable is vaccination status (vaccinatedversusunvaccinated). The dependent variable is health outcome with two levels:

• Contracted pneumoccal pneumonia;
• Did not contract pneumonia.

The company wanted to know if providing the vaccine made a difference. To answer this question, they must choose a statistic that can test for differences when all the variables are nominal. The ²statistic was used to test the question, "Was there a difference in incidence of pneumonia between the two groups?" At the end of the winter, Table 1 was constructed to illustrate the occurrence of pneumonia among the employees.

Table 1. Results of the vaccination program.

Health Outcomes

Unvaccinated Vaccinated Total

Sick w/ pneumococcal pneumonia 23 7 30

No pneumonia 61 77 138

Total 84 84 168

What are the null and alternate hypotheses?

What is the observed calculated Chi square result?

What is the degree of freedom?

What is the start of the critical region?

Reject the null hypothesis?

What is the analysis of this result?