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Handout3, Chapter9, Section 2 – ph6450
What is the appropriate test?
[Examples adapted from: Moore and McCabe, Introduction to the Practice of Statistics;
Diane Essex-Sorlie, Medical Biostatistics and Epidemiology; Glanz, Primer of
Biostatistics]
For each scenario below:
1. Identify the sample or samples and how they are formed.
2. Indicate the type of outcome variable (categorical, continuous).
If the outcome is categorical indicate if it is dichotomous, ordinal
or nominal.
3. Choose an appropriate test.
Normal approximation to the binomial (for counts, one
proportion, or the difference of proportions).
Chi-square test (independence or homogeneity)
Binomial exact test (for counts)
Z or T test (one mean or difference of means)
A. Two pediatricians wish to test the effectiveness of an educational program that
provides information to parents about the benefits of childhood immunizations.
The researchers hypothesize that parents who participate in the program are more
likely to have their children immunized, verses parents who do not participate. Two
samples of parents and their children are formed randomly from records of a family
practice clinic. One sample of parents participates in the program. Of the 93
parents who participate, 73 go on to obtain a full set of immunizations for their
child. Of the 71 parents who do not participate in the program, 30 go on to obtain a
complete set of immunizations for their child.
B. Seventy percent of a specified population are not immune to gastroenteritis caused
by a retrovirus. If a random sample of 10 people is randomly selected from this
population, what is the probability that fewer than 7 people are not immune?
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C. In a study of heart surgery, one issue was the effect of drugs called beta-blockers,
on the pulse rate of patients during surgery. The subjects were divided at random
into two groups of 30 patients each. One group received a beta-blocker; the other, a
placebo. The pulse rate of each patient at a critical point during the operation was
recorded. The treatment group had a mean of 65.2 and a standard deviation of 7.8.
For the control group, the mean was 70.3 and a standard deviation of 8.3. Do betablockers create a change in pulse-rate?
D. The occurrence of dementia in patients, age 60 and older, with idiopathic
Parkinson’s disease was investigated to determine if dementia occurs with greater
frequency in this age than in the general population. Four percent of individuals in
this age group in the general population have dementia. 272 patients age 60 years
and older, with idiopathic Parkinson’s disease were examined; 36 exhibited
dementia.
E. Three populations of women in medicine are randomly sampled to determine if
difference exist with respect to satisfaction with medicine as a career choice
(yes/no). 56 of 100 first-year female medical students say they are satisfied with
their choice of medicine as a career. 58 of 100 female residents express
satisfaction. 38 of 100 practicing female clinicians, out of residency at least 3
years, indicate satisfaction.
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F. Investigators at the Children’s Defense Fund believe that the rapid progress in
maternal and child health in the 1960s, 1970s and through the mid-1980s has “been
brought to a screeching halt.” In 1970, 7% of infants were low-birthweight babies.
It is hypothesized than an increase will be observed in 2006, compared to 1970, in
the proportion of babies with low birthweights. In a random sample of 20 newborns
at a large metropolitan Mid-western hospital, 5 were identified as low birthweight
infants.
G. Psychological and social factors can influence the survival of patients with serious
disease. One study examined the relationship between coronary heart disease
(CHD) and pet ownership. Each of 92 patients was classified as having a pet or not
and by whether they survived for one year. Of the 53 pet owners 50 survived one
year. Of the 39 who did not own pets, 28 survived one year. Do pet ownership and
one-year survival appear to be associated?
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H. To assess the occurrence of restenosis following balloon angioplasty to open
clogged coronary arteries, investigators conducted a multicenter, follow-up study
involving several thousand patients. The researchers found that 6 months after
balloon angioplasty, 80% of patients had stenosis limited to 50% or less of baseline.
A relatively new procedure, directional atherectomy, is used sometimes to excise
atherosclerotic plaque from coronary arteries. In a random sample of 100 patients
who underwent directional atherectomy, 89 had stenosis limited to 50% or less of
baseline 5 months after surgery. Based on these data, how does directional
atherectomy compare with balloon angioplasty with respect to the proportion of
patients who have restenosis?
I. Irradiation to symptomatic areas, combined with intrathecal methotrexate, is the
conventional treatment for neoplasms that metastasize to the leptomenginges.
Long-term prognosis, however, is poor: only 10% of patients survive 12 months.
In a South American clinic, 12 patients with carcinomatous meningitis receive an
experimental treatment that couples irradiation with intrathecal methotrexate with
dietary management and herbal remedies. The goal is to determine if the
experimental regimen increases 12-month survival. Twelve months later, two
patients who received the experimental treatment are alive.
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J. In a clinic in a large city on the West Coast, men who are HIV-positive,
asymptomatic, and have CD4+ cell counts above 400/mL3 are chosen randomly to
receive zidovudine or placebo for 36 months. Participants are followed to
determine if fewer patients receiving zidovudine experience disease progression to
AIDS or death. Seventy-eight of 300 men receiving zidovudine and 111 of 300
men receiving placebo experience disease progression or death.
K. Diabetics often have an abnormality of the capillary basal lamina (basement
membrane) characterized by added layers and increased thickness of the lamina,
which are detected easily in the major capillary beds of skin and skeletal muscle. A
preliminary clinical trial was conducted to determine the effectiveness of an
experimental drug to treat this abnormality in randomly sampled diabetics. Forty
diabetics were treated with the drug for 2 years; the mean thickness of the capillary
basal lamina at the end of the treatment period was 161.o mm (s=10.2). Thirty four
diabetics received an apparently – identical placebo for 2 years; for the placebo
group, the mean thickness was 170.9 mm (s=14.7) at the end of two years. Do
these means differ significantly? Assume the population distributions are normal.
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