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1. In a study, 28 adults with mild periodontal disease are assessed before and 6 months after the implementation of a dental-education program intended to promote better oral hygiene. After 6 months, periodontal status improved in 15 patients, declined in 8, and remained the same in 5.

Choose one answer:

Assess the impact of the program statistically (use a two-sided test).

We do not reject H_0 at the 5% level and conclude that patients have not significantly changed on the program.

We reject H_0 at the 5% level and conclude that patients have significantly changed on the program.

We reject H_0 at the 5% level and conclude that patients have not significantly changed on the program.

We do not reject H_0 at the 5% level and conclude that patients have significantly changed on the program.

2. data can be ordered but do not have specific numeric values. Thus, common arithmetic cannot be performed on ordinal data in a meaningful way.

Choose one answer:

ordinal

interval

ratio

nominal

3. A ______________ design is a type of randomized clinical trial in which each participant is randomized to either group A or group B which receive different treatments, then later switch treatments.

Choose one answer:

cross-over

case-control

prospective

retrospective

4. Suppose researchers do an epidemiologic investigation of people entering a sexually transmitted disease clinic. They find that 160 of 200 patients who are diagnosed as having gonorrhea and 50 of 105 patients who are diagnosed as having nongonococcal urethritis have had previous episodes of urethritis.

Are the present diagnosis and prior episodes of urethritis associated? (Hint: a chi-square test with Yates' correction)

Choose one answer:

Gonorrhea patients are significantly more likely to have prior episodes of urethritis than NGU patients.

Gonorrhea patients are not significantly more likely to have prior episodes of urethritis than NGU patients.

5. The _______ rate is defined as the proportion of participants in the placebo group who actually receive the active treatment outside the study protocol.

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9. For any sample point ( x subscript i, y subscript i), the ___________________ of that point about the regression line is defined by ( stack y subscript i with hat on top minus top enclose y). (Hint: the blank is two words)

10. The following statistics are taken from an article by Burch relating cigarette smoking to lung cancer. The article presents data relating mortality from lung cancer to average cigarette consumption (lb/person) for females in England and Wales over a 40-year period. The data are given in the table below.

Cigarette consumption and lung-cancer mortality in England and Wales, 1930-1969

Period	log_{10} mortality (over 5 years), y	log_{10} annual cigarette consumption (lb/person), x
1930-1934	-2.35	-0.26
1935-1939	-2.20	-0.03
1940-1944	-2.12	0.30
1945-1949	-1.95	0.37
1950-1954	-1.85	0.40
1955-1959	-1.80	0.50
1960-1964	-1.70	0.55
1965-1969	-1.58	0.55

Source: Based on the Journal of the Royal Statistical Society, A., 141, 437-477, 1978.

Compute the correlation between 5-year lung-cancer mortality and annual cigarette consumption when each is expressed in the log_{10} scale.

11. A ____________ variable is a variable that is associated with both the disease and the exposure variable. Such a variable must usually be controlled for before looking at a disease-exposure relationship.

Choose one answer:

confounding

random

discrete

continuous

12. Researchers compare protein intake among three groups of postmenopausal women: (1) women eating a standard American diet (STD), (2) women eating a lacto-ovo-vegetarian diet (LAC), and (3) women eating a strict vegetarian diet (VEG). The m e a n space plus-or-minus space 1 space s d for protein intake (mg) is presented in the table below.

Protein intake (mg) among three dietary groups of postmenopausal women

Group Mean sd n

STD 75 9 10

LAC 57 13 10

VEG 47 17 6

Perform a statistical procedure to compare the means of the three groups using the critical-value method. Report the p-value from this test.

13. In a 1985 study of the relationship between contraceptive use and infertility, 89 of 283 infertile women, compared with 640 of 3833 control (fertile) women, had used an intrauterine device (IUD) at some time in their lives.

Use the normal-theory method to test for significant differences in contraceptive-use patterns between the two groups.

Choose one answer

The difference in previous IUD usage rates is highly significant with cases significantly more likely to have previously used an IUD than controls, with p<0.001.

The difference in previous IUD usage rates is highly significant with cases significantly more likely to have previously used an IUD than controls, with p<0.01.

The difference in previous IUD usage rates is not significantly more likely to have previously used an IUD than controls, with p<0.001.

The difference in previous IUD usage rates is not significantly more likely to have previously used an IUD than controls, with p<0.01.

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17. A negative confounder is a variable that either

Choose one answer:

is postively associated with both exposure and disease

is negatively associated with disease and positively associated with exposure

is positively associated with disease and negatively associated with exposure

is negatively associated with both exposure and disease

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19. Consider the information from Problem 18. Two hundred subjects are selected randomly from the population and followed for various lengths of time. The average length of follow-up is 1.5 years. Suppose that at the end of the study, the estimated rate is 4 per 100 person-years. How many events must have been observed in order to yield the estimated rate of 4 per 100 person-years?

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