Assignment: Computation by Hand

Answer question 1 using data in table 1 below.

Table 1:

• Compute the simple odds ratio of the association of donor’s sex and survival status of the infant. Be sure to answer all four parts to this question (a, b, c, and d), including manual calculation of the chi-square value

a. Manually calculate a simple odds ratio to test the hypothesis of no association between donor’s sex and the survival status of the infant, without the inclusion of the variable severity using a 2 x 2 table for sex and survival

b. Manually calculate the confidence interval associated with that odds ratio using the appropriate formula

c. Manually compute the Chi Square test statistic for this table

d. Interpret the results. Include an interpretation of the odds ratio, the confidence interval, and the Chi Square test statistic in your

Table 2:

• Using data in table 2, compute the common odds ratio of the association between donor’s sex and the survival status of the infant, after controlling for severity

a. Manually calculate a common odds ratio to test the hypothesis of no association between donor’s sex and the survival status of the infant, after the inclusion of the variable severity using the common odds ratio

b. Interpret the results. How does the common odds ratio differ from the simple odds ratio computed in part 1? What effect might it have on your decision from part 1 to reject or fail to reject the null hypothesis?

c. Why is it important to know the effect of severity on the association of gender and survival?

• Perform a simple logistic regression using SPSS and the Week 6 Dataset (SPSS document). Answer the following questions based on your SPSS output

a. Are the results of the simple logistic regression similar to or different from the results of the simple odds ratio?

b. How are they similar or different? Include output from SPSS and an interpretation of the OR and confidence intervals in your response

c. What can you do using logistic regression to duplicate the results from part 2 of this application (the use of CMH for common odds)

Resources

Daniel, WW & Cross, CL. (2013). Biostatistics: A Foundation for Analysis in the Health Sciences. Hoboken, NJ: Wiley.

• Chapter 11, “ Regression Analysis: Some Additional Techniques” ( pp. 539 –599)
• Chapter 12, “Chi Square Distributions” ( pp. 600 –669)