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648 CHAPTER 12 THE CHI-SQUARE DISTRIBUTION AND THE ANALYSIS OF FREQUENCIES
What is the estimated odds ratio of having rhinitis among subjects with a family history of an
unbalanced diet compared to those eating a balanced diet Compute the 95 percent confidence
interval for the odds ratio.
12.7.5 According to Holben et al. (A-22), “Food insecurity implies a limited access to or availability of
food or a limited/uncertain ability to acquire food in socially acceptable ways.” These researchers
collected data on 297 families with a child in the Head Start nursery program in a rural area of
Ohio near Appalachia. The main outcome variable of the study was household status relative to
food security. Households that were not food secure are considered to be cases. The risk factor of
interest was the absence of a garden from which a household was able to supplement its food supply.
In the following table, the data are stratified by the head of household’s employment status
outside the home.
Stratum 1 (Employed Outside the Home)
Risk Factor Cases Noncases Total
No garden 40 37 77
Garden 13 38 51
Total 53 75 128
Stratum 2 (Not Employed Outside the Home)
Risk Factor Cases Noncases Total
No garden 75 38 113
Garden 15 33 48
Total 90 71 161
Source: David H. Holben, Ph.D. and John P. Holcomb, Jr., Ph.D. Used with permission.
Compute the Mantel–Haenszel common odds ratio with stratification by employment status. Use
the Mantel–Haenszel chi-square test statistic to determine if we can conclude that there is an association
between the risk factor and food insecurity. Let a = .05.
12.8 SURVIVAL ANALYSIS
In many clinical studies, an investigator may wish to monitor the progress of patients
from some point in time, such as the time a surgical procedure is performed or a treatment
regimen is initiated, until the occurrence of some well-defined event such as death
or cessation of symptoms.
Suppose, for example, that patients who have experienced their first heart attack
are enrolled in a study to assess the effectiveness of two competing medications for the
prevention of a second myocardial infarction. The investigation begins when the first
patient, following his or her first heart attack, is enrolled in the study. The study continues
until each patient in the study experiences one or another of three events: (1) a
myocardial infarction (the event of interest), (2) loss to follow-up for some reason such
as death from a cause other than a heart attack or having moved to another locality, or