Introductory Biostatistics

of positive tuberculin reaction separately for each of the two subpopula-

tions, those with high exposure and those with low exposure.

TABLE E4.6

Exposure Level Number Tested Number Positive

High 129 63

Low 325 36

4.7 The prevalence rates of hypertension among adult (ages 18–74) white
and black Americans were measured in the second National Health
and Nutrition Examination Survey, 1976–1980. Prevalence estimates
(and their standard errors) for women are given in Table E4.7. Calculate
and compare the 95% confidence intervals for the proportions of the two
groups, balcks and whites, and draw appropriate conclusion. Do you
need the sample sizes to do your calculations?

TABLE E4.7

p(%) SE(p)

Whites 25.3 0.9

Blacks 38.6 1.8

4.8 Consider the data given in Table E4.8. Calculate the 95% confidence
intervals for the sensitivity and specificity of x-ray as a screening test for
tuberculosis.

TABLE E4.8

Tuberculosis

X-ray No Yes Total

Negative 1739 8 1747

Positive 51 22 73

Total 1790 30 1820

4.9 Sera from a T-lymphotropic virus type (HTLV-I) risk group (prostitute
women) were tested with two commercial research enzyme-linked
immunoabsorbent assays (EIA) for HTLV-I antibodies. These results
were compared with a gold standard, and the outcomes are shown in
Table E4.9. Calculate the 95% confidence intervals for the sensitivity and
specificity separately for the two EIAs.

EXERCISES 175