Statistics/Epi

Question 1

The total Population disease burden at a specific point in time is referred to as the:

a. ratio
b. mortality
c. incidence
d. prevalence
e. attributable fraction

Answer 1

D. Prevalence

Question 2

Herd immunity is least affected by:

a. antigenic portion of the agent.
b. antigenic stability of the agent.
c. serologic epidemiology.
d. random distribution of immune individuals within the herd.
e. movements of individuals within the population.

Answer 2

c. serologic epidemiology

Question 3

Which of the following characteristics of a biological agent is most likely to be seen in a disease which occurs in epidemic proportions?

a. High infectivity.
b. High pathogenicity.
c. High virulence.
d. Low antigenicity.
e. Viability.

Answer 3

a. High infectivity

Question 4

Brucellosis, a bacterial zoonosis, and Q Fever, a rickettsial zoonosis, have one important epidemiological characteristic in common:

a. both have a high mortality rate in animals.
b. both are transmitted by swine.
c. they can be prevented by vaccination.
d. both cause pulmonary disease in man.
e. the reproductive and accessory reproductive organs serve as the principle source of environmental contamination.

Answer 4

e. the reproductive and accessory reproductive organs serve as the principle source of environmental contamination.

Question 5

Which one of the following frustrations would you most likely expect in preparing to carry out cohort studies on animal disease?

a. Costly and time consuming, and plagued by the continual changing of the cohort.
b. Difficult time in selecting a comparison group or control population upon which to test your hypothesis.
c. Cohort populations are unchanging, and that no new individuals are introduced into the study population.
d. Data collected retrospectively is often incomplete, and plagued by high degrees of institutional bias.
e. Unable to get accurate estimates of incidence or prevalence of the disease using the cohort study technique.

Answer 5

a. Costly and time consuming, and plagued by the continual changing of the cohort

Question 6

A measure of the spread of an infectious disease among susceptibles following exposure to a primary case is known as the:

a. period prevalence rate.
b. secondary attack rate.
c. proportional attack rate.
d. morbidity rate.
e. prevalence rate.

Answer 6

b. secondary attack rate.

Question 7

The time necessary after acquisition of infection for an agent to multiply sufficiently to be transmitted by an arthropod is the:

a. extrinsic incubation period.
b. infectivity period.
c. vector circadian period.
d. pre-latent period.
e. latent period.

Answer 7

a. extrinsic incubation period

Question 8

The term “3 host tick” refers to:

a. ticks can carry infection to only three species of animals.
b. ticks can carry three different diseases at one time.
c. the tick goes through feeding of blood meals on three different hosts to complete its life cycle.
d. the adult tick can live three years on one host.
e. the larval stage must feed on three different hosts to complete cycle.

Answer 8

c. the tick goes through feeding of blood meals on three different hosts to complete its life cycle

Question 9

Using the following 2X2 display, which relationship correctly depicts the specificity of a diagnostic test?
DZ NO DZ
+ A B A+B
- C D C+D
A+C B+D

a. A/(C+D)
b. D/(A+B)
c. A/(A+C)
d. D/(B+D)
e. A/(C+D)

Answer 9

d. D/(B+D)

Question 10

A disease which tends to be localized in space and time is called:

a. outbreak.
b. sporadic.
c. enzootic.
d. pandemic.
e. epizootic.

Answer 10

a. outbreak.

Question 11

What study plan would be best to determine the effectiveness of a new vaccine in preventing disease in humans?

a. Case-control study.
b. Cohort study.
c. Prevalence study.
d. Morbidity study.
e. Retrospective study.

Answer 11

b. Cohort study.

Question 12

A certain causal factor is thought to be associated with an extremely rare disease. What study plan would yield the best data with limited financial and human resources.

a. Prevalence study.
b. Case-control study.
c. Prevalence study.
d. Morbidity study.
e. Case evaluation study.

Answer 12

b. Case-control study.

Question 13

Which of the following factors is least likely to influence the rate of spread of a disease?

a. Infectivity of the agent.
b. Number of susceptible hosts.
c. Number of sources.
d. Virulence of the agent.
e. Percentage of immunes.

Answer 13

d. Virulence of the agent.

Question 14

When considering instituting a vaccine program against a particular disease, which of the following factors should be of least concern?

a. local prevalence of disease.
b. viability of disease agent.
c. immunogenicity of vaccine.
d. antigenic stability of the agent.
e. exposure potential of the herd.

Answer 14

b. viability of disease agent

Question 15

One of your clients has a feedlot containing 15,000 cattle, 10,000 of which are susceptible. In a current outbreak of disease, 3,000 became sick and 300 died. The case fatality rate was:

a. 10%
b. 25%
c. 2%
d. 30%
e. 3%

Answer 15

a. 10%

Question 16

An organism which is highly immunogenic can still produce a second infection in the same individual if it has high:

a. pathogenicity.
b. virulence.
c. antigenicity.
d. mutability.
e. antigenic portion.

Answer 16

d. mutability

Question 17

The essential difference between infection and disease is:

a. immune status.
b. pathogenicity.
c. virulence.
d. portal of entry.
e. shedding of organism.

Answer 17

b. pathogenicity

Question 18

You are studying a group of 25 cattle, 20 angus and 5 Holsteins. Using a table of random numbers you select a sample of 5 cattle from the population. They turn out to be 5 Holsteins. This is a:

a. representative sample.
b. random sample.
c. stratified random sample.
d. invalid sample.
e. personally biased sample.

Answer 18

b. random sample

Question 19

The point of maximum concentration in an array of numbers is the:

a. mode.
b. mean.
c. median.
d. average.
e. variance.

Answer 19

a. mode

Question 20

If an effective vaccine were applied to a secularly cycling disease it would:

a. decrease the number of cases.
b. shorten the cycle.
c. extend the seasonal pattern.
d. shorten the seasonal pattern.
e. eliminate the cycle.

Answer 20

a. decrease the number of cases

Question 21

An incidence that is usually expressed as a percent, used for particular populations, and observed for limited periods of time, as in an epidemic, is known as:

a. prevalence rate.
b. adjusted rate.
c. index.
d. attack rate.
e. ratio.

Answer 21

d. attack rate

Question 22

In a disease control program based on practitioner reporting, the greatest obstacle to success will be diseases with:

a. high case fatality rate.
b. many subclinical infections.
c. long convalescent carrier state.
d. short term immunity.
e. a low virulence.

Answer 22

b. many subclinical infections

Question 23

In determining the potential for spread of a newly recognized disease, it is important to know the:

a. period of viremia.
b. duration of clinical illness.
c. serological response.
d. response to therapy.
e. period of transmissibility.

Answer 23

e. period of transmissibility

Question 24

In vertical transmission, the source is the:

a. parent.
b. sibling.
c. pet.
d. food.
e. vehicle

Answer 24

a. parent

Question 25

Which of the following is least important in determining human exposure to Tularemia?

a. Individual’s preference for goat milk.
b. Number of ticks in the environment.
c. Duration of bacteremia in the reservoir.
d. Occupation.
e. Vector density.

Answer 25

a. Individual’s preference for goat milk

Question 26

To be significant, the titer difference between paired sera should be at least:

a. two fold.
b. four fold.
c. ten fold.
d. four dilutions.
e. four tubes.

Answer 26

b. four fold

Question 27

Environmental manipulation has the least probability for being an effective means of infectious disease control when the following type of transmission is involved:

a. vehicle.
b. vector.
c. transtadial.
d. arthropod borne.
e. contact.

Answer 27

e. contact

Question 28

The measure most sensitive to extremes is:

a. mean.
b. median.
c. mode.
d. sample.
e. inferential.

Answer 28

a. mean

Question 29

Objectivity is best assured by:

a. representative nature.
b. randomness.
c. sample size.
d. precise manipulation.
e. statistical validity.

Answer 29

b. randomness

Question 30

Which of the following is NOT associated with a retrospective study?

a. Adaptable to conditions of low prevalence.
b. Less expensive than prospective.
c. Requires fewer personnel.
d. Takes longer to conduct.
e. Provides less accurate incidence rate.

Answer 30

d. Takes longer to conduct

Question 31

An infant has become acutely ill and cultures of its blood and stool are positive for Salmonella typhimurium. An epidemiologist investigating the cause makes the following notes. Which one is most likely to contain the clue to the etiology of this case?

a. The father, who had been away on a “white-water” canoe trip for ten days, had a headache and felt weak while playing with the infant nine hours before it became ill. A short time later he developed “indigestion”.
b. About ten hours before the onset of illness the infant was bitten by an insect. From the description given of the insect it was probably Chrysops discalis. The physician who attended the child the following morning noted a red swollen area at the site of the bite.
c. Two days before the illness the family cat, which was known as a good “mouser”, scratched the infant.
d. Nineteen hours before the onset of illness the mother cleaned and stuffed a chicken. As soon as she finished that chore she prepared the infant formula which was fed to it thirty minutes later.
e. Seven days prior to the illness the infant was taken on a short visit to the home of its grandmother. The water for the house came from an artesian well and while visiting the infant was given some of the untreated water.

Answer 31

D. Nineteen hours before the onset of illness the mother cleaned and stuffed a chicken. As soon as she finished that chore she prepared the infant formula which was fed to it thirty minutes later.

Question 32

Listed below are five test procedures which are useful in the identification of enteric organisms. Which one is especially useful for determining the origin of epidemics?

a. Fermentation studies.
b. Antigenic analysis.
c. Selective growth media.
d. Paired-sera comparison tests.
e. Staining of organisms.

Answer 32

b. Antigenic analysis

Question 33

To determine if the observed difference between the means of two frequency distributions is statistically significant, one needs to know the:

a. standard error of measurement of each distribution.
b. true mean of each distribution.
c. standard error of the mean of each distribution.
d. standard error of the correlation of the two distributions.
e. median of each distribution.

Answer 33

c. standard error of the mean of each distribution

Question 34

Two broad categories of inquiry by observation are the prospective and the retrospective approaches. In comparing these approaches it agreed that:

a. the retrospective approach is likely to give results faster.
b. in the prospective approach, the sample can be clearly defined and bias factors recognized.
c. in the prospective approach incidence rates can be easily calculated and compared.
d. All of the above.
e. None of the above.

Answer 34

d. All of the above.

Question 35

A veterinary practitioner has been called upon by local livestock owners to discuss a newly introduced exotic disease for which there is a vaccine and a national program for eradication of the disease. In response to questions about the use of vaccines, either as part of the program or as protection for individual herds, he/she should make the following statement:

a. If vaccines (polio, mumps, whooping cough, etc) are good enough for people they are good enough for animals.
b. Vaccines vary widely as to their efficacy, ability to mask disease, potential for creating disease and costs. They should be considered in these lights before being used.
c. Vaccines are thoroughly tested before being used and would not be offered for use by the public if they had serious objectional features.
d. Vaccines are the key to an eradication program.
e. All of the above.

Answer 35

b. Vaccines vary widely as to their efficacy, ability to mask disease, potential for creating disease and costs. They should be considered in these lights before being used

Question 36

The following data were collected in 1978 during an outbreak of winter dysentery in a herd of 33 dairy cattle in Groton, New York.  Animals recovered or died within 5 days of onset. 
 DATE		# NEW CASES	# DEATHS
January 18		1			0
January 19		1			1
January 20		6			0
January 21		3			3
January 22		3			2
January 24		2			0
January 26		1			1
Suppose you suspected the outbreak was due to a farm visitor and you obtained a history of exposure of the herd by interviewing the dairy owner.  Assuming that the average incubation period for the disease was five days, with a range of 2 to 11 days, which source of exposure best supports the hypothesis that the outbreak was attributable to a common source?

Visitor Dates on the farm

a. Cattle trucker January 13
b. Veterinarian January 1, 14, and 20
c. Neighbor farmer January 7, 13, and 23
d. Commune dweller with diarrhea January 10
e. Inseminator January 15

Answer 36

e. Inseminator January 15

Question 37

An epidemiologic study tests the following hypothesis: There is no association between having a pet dog in the household and the occurrence of multiple sclerosis (ms) in a household resident.” The study utilizes a case-control procedure and the results are:
Odds ratio = 2.62; 95% confidence interval = 0.9 - 5.26

The correct conclusion is:

a. Reject the null hypothesis.
b. Accept the null hypothesis.
c. Accept the alternative hypothesis.
d. The ms incidence rate in the exposed group is 2.62 times the ms incident rate in the nonexposed group.
e. The study is statistically significant at the 5% level.

Answer 37

b. Accept the null hypothesis

Question 38

Assume that the incidence of a disease is declining while the prevalence (measured at interval) remains essentially the same over a given time period.
Which of the following explanations is the most plausible?
a. Recovery from the disease is becoming more rapid.
b. The disease is highly fatal but can not be considered epidemic.
c. The disease is becoming shorter in duration with an increase in mortality.
d. Preventive measures have failed but there is less case-fatality.
e. The disease is becoming more chronic with a decrease in mortality.

Answer 38

e. The disease is becoming more chronic with a decrease in mortality

Question 39

You examine a flock of 500 ewes and find evidence of foot rot in 100 ewes. The incidence rate of foot rot in this flock is:

a. 20%
b. 17%
c. 83%
d. unknown.

Answer 39

d. unknown

Question 40

An epidemic curve displays:

a. the population at risk versus the frequency of cases.
b. the frequency of cases versus the number of ill in the population.
c. the time of onset versus the population at risk.
d. the time of onset versus the frequency of incident cases.
e. the time of onset versus the number of individuals who are ill.

Answer 40

d. the time of onset versus the frequency of incident cases

Question 41

A decrease in the prevalence of a disease could be interpreted as a result of:

a. a reduction in the incidence.
b. a more rapid cure.
c. a shorter life span of affected individuals.
d. “a” and “c” above.
e. All of the above.

Answer 41

e. All of the above

Question 42

Which of the following is NOT typical of a cohort study?

a. The attribute (independent variable) may not be as well recorded in those who do not develop the disease.
b. It is usually a long, expensive and major undertaking.
c. The classification of individuals with regard to the attribute (independent variable) may change during the course of the study.
d. Incidence rate and relative risk can usually be calculated directly.
e. it is usually a prospective study and therefore attrition can be a serious problem.

Answer 42

a. The attribute (independent variable) may not be as well recorded in those who do not develop the disease.