6.12 Epidemic keratoconjunctivitis (EKC) or ‘‘shipyard eye’’ is an acute
infectious disease of the eye. A case of EKC is defined as an illness con-
sisting of redness, tearing, and pain in one or both eyes for more than
three days’ duration, diagnosed as EKC by an ophthalmologist. In late
October 1977, one (physician A) of the two ophthalmologists providing
the majority of specialized eye care to the residents of a central Georgia
county (population 45,000) saw a 27-year-old nurse who had returned
from a vacation in Korea with severe EKC. She received symptomatic
therapy and was warned that her eye infection could spread to others;
nevertheless, numerous cases of an illness similar to hers soon occurred
in the patients and sta¤ of the nursing home (nursing home A) where she
worked (these people came to physician A for diagnosis and treatment).
Table E6.12 provides exposure history of 22 persons with EKC between
October 27, 1977 and January 13, 1978 (when the outbreak stopped,
after proper control techniques were initiated). Nursing home B, in-
cluded in this table, is the only other area chronic-care facility. Using an
appropriate test, compare the proportions of cases from the two nursing
homes.
TABLE E6.12
Exposure Cohort Number Exposed Number of Cases
Nursing home A 64 16
Nursing home B 238 66.13 Consider the data taken from a study that attempts to determine
whether the use of electronic fetal monitoring (EFM) during labor
a¤ects the frequency of cesarean section deliveries. Of the 5824 infants
included in the study, 2850 were monitored electronically and 2974 were
not. The outcomes are shown in Table E6.13. Test to compare the rates
of cesarean section delivery, EFM-exposed versus nonexposed; state
clearly your null and alternative hypotheses and choice of test size.
TABLE E6.13
EFM Exposure
Cesarean
Delivery Yes No
Yes 358 229
No 2492 2745
Total 2850 29746.14 A study was conducted to investigate the e¤ectiveness of bicycle safety
helmets in preventing head injury. The data consist of a random sample
238 COMPARISON OF POPULATION PROPORTIONS