Suggested answers to exercise: Cough during the day or at night and history of bronchitis, 3

Question 3: Now make cough the row variable and history of bronchitis the column variable. (This was how the table was presented in the lecture.) Carry out the chi-squared test of association and calculate the odds ratio and the relative risk. How do the results change?

Suggested answer

We choose Analyze, Descriptive Statistics, Crosstabs. Put the variable 'Bronchitis by age 5' into Row(s): and 'Day or night cough at age 12' into Column(s):. Click Statistics, Chisquare, Continue. Click OK.

You should get the case processing summary and then the following:

Day or night cough at age 12 * Bronchitis by age 5 Crosstabulation
Count
		Bronchitis by age 5		Total
		Yes	No
Day or night cough at age 12	Yes	26	44	70
	No	247	1002	1249
Total		273	1046	1319

Chi-Square Tests
	Value	df	Asymp. Sig. (2-sided)	Exact Sig. (2-sided)	Exact Sig. (1-sided)
Pearson Chi-Square	12.180a	1	.000
Continuity Correctionb	11.145	1	.001
Likelihood Ratio	10.609	1	.001
Fisher's Exact Test				.001	.001
Linear-by-Linear Association	12.171	1	.000
N of Valid Cases	1319
a 0 cells (.0%) have expected count less than 5. The minimum expected count is 14.49
b Computed only for a 2x2 table

Risk Estimate
	Value	95% Confidence Interval
		Lower	Upper
Odds Ratio for Day or night cough at age 12 (Yes / No)	2.397	1.448	3.970
For cohort Bronchitis by age 5 = Yes	1.878	1.358	2.598
For cohort Bronchitis by age 5 = No	.784	.653	.940
N of Valid Cases	1319

There are the following differences:

1. In the cross-tabulation, the rows have become the columns and the columns have become the rows, as we requested.
2. The odds ratio row in the Risk Estimate table has a different label, but the numbers are the same as before.
3. The second and third rows in the Risk Estimate table have different labels and different numbers in them.

Back to Exercise: Cough during the day or at night and history of bronchitis.

To Applied Biostatistics index.

To Martin Bland's M.Sc. index.

To Martin Bland's home page.

This page maintained by Martin Bland.
Last updated: 20 February, 2012.

Back to top.