Epidemiology Midterm / F99

Coverage: Chapter 1 - 6

Instructions: Read each question carefully. For multiple-choice questions, provide the single best response. For open-ended questions, please be brief, accurate, and concise. For calculation questions, show all work. Point values are in [square brackets]. Time limit: 60 minutes.

1. Define "epidemiology."

study of / disease and related-events / in populations / and application of this study to the prevention and control of health problems.

2. Define "public health."

organized activity / to prevent disease and promote health

3. Name two ways in which hard sciences differ from soft sciences.

hard science more likely to use objective measures
hard science less likely to study human directly

4. Define "epidemic."

disease occurrence / in clear excess of normalcy

5. What is currently the leading cause of death in the U. S.?

cardiovascular disease

6. What is currently the third leading cause of death in the U. S.?

external cause

7. Define "natural history of disease."

progress of a disease / in an individual / over time

8. The habitat or environment in which an infectious agent lives and multiplies is referred to as its ________________________.

reservoir

9. The time period between exposure to an ultimate agent and the first symptoms is called the _____________________ period.

incubation, latent, or subclinical

10. Define "cause" from an modern epidemiologic perspective. [2]

Any factor that increases the likelihood of disease / all other things being equal (caetaris paribis)

11. An epidemic curve shows a sharp increase followed by a plateau or continuing increase. This pattern is typical of a __________ epidemic.

propagating

12. How does "infection" differ from "infectious disease"?

many infections are asymptomatic; diseases always have signs or symptoms, or are associated with a dysfunction

13. Match the following four terms with their definition, below: causal-web model; contributing factor; pathogenicity; infectivity [1 pt each].
Definition Term
The ability of an agent to cause disease within a host. pathogenicity
The ability of an agent to enter and establish itself within a host. infectivity
A factor that is neither necessary nor sufficient, but nevertheless increases the likelihood of disease. contributing factor
A theory of causality that suggests direct and indirect causes of disease are linked in a complex and interrelated hierarchy. causal-web

14. List the elements of the infectious disease process

agent; reservoir; portals; transmission; immunity

15. What is the difference between a vaccine an a toxoid? [2 pts]

vaccine - immunized against the agent
toxoid - immunized against the poison produced by the agent

16. List an example of an innate chemical form of immunity.

Any of following: pH of stomach or vaginal; gastrointestinal enzymes; interferon; lipids that create inhospitable environment

17. What does NK stand for in the immunocyte referred to as an "NK cell." [1]

natural killer

18 . The two general of vaccines are "killed" and "____________________ live." [1]

modified (or attenuated)

21. Name two types of chronic diseases studied by epidemiologists. [2]

There are many (e.g., cardiovascular, cancer, lung, diabetes, metabolic, musculoskel, neuro, ...)

Two raters independently review 100 patients for the presence of a condition. They find:

Rater B
Rater A + -
+ 10 5 15
- 5 80 85
15 85 100

22. Calculate the kappa statistic [3]:

kappa = .6078 (calculations not shown on Web)

23. The above kappa statistic indicates:

a. Poor agreement
b. ***Fair to good agreement***
c. Excellent agreement
24. Why is the above considered a reproducibility analysis (and not a validity analysis)? [1]

two independent raters w/ no gold standard

25. True or False: Signs are indicators of disease reported by patients. [1] _______________

False (symptoms are reported by the patient)

26. What does "ICD" stand for? [1]

International Classification of Disease

27. We start with a population of 1,000 individuals in which the prevalence of disease is 10% (.1). Suppose a test that is 99% sensitive (SEN = .99) and 97% specificity (SPEC = .97) is used in this population. Based on this information, fill in the "validity table" below. [5 pts]

D+ D-
T+ TP FP n1
T- FN TN n2
m1 m2 1,000

m1 = (.1)(1000) = 100
m2 = 1000 - 100 = 900
TP = (.99)(100) = 99
FN = 100 - 99 = 1
TN = (.97)(900) = 873
FP = m2 - TN = 900 - 873 = 27

28. Why is the above problem (#27) considered a validity analysis (and not a reproducibility analysis)? [1 pt]

Test results are compared to a gold standard.

29. Assuming we are dealing with the usual situation in which there is an overlap in test score values in healthy and diseased populations, and the diseased population tends to have higher values on the test compared with the healthy population, will there be an increase, decrease, or no change in the number of false negatives when we decrease the cutoff point for positive test results? [1]

a. Increase
b. ***Decrease***
c. No change

30. Continuing with the scenario drawn in #29, above, how will this effect the number of false positives? [1]

a. ***Increase***
b. Decrease
c. No change

31. Other than sensitivity and specificity, what determines the predictive value positive of a diagnostic test?

Prevalence or "prior probability of disease"

32. What will happen to the prevalence of a disease when a new treatment is developed that prevents death but does not produce recovery? (Assume incidence remains constant.)

a. Prevalence will decrease
b. ***Prevalence will increase***
c. Prevalence will remain constant

33. Identify one way in which incidence differs from prevalence? [2]

Many choices (see Table 6.2, p. 97).

34. We begin a study and find 75 of the 250 study subjects have the disease in question. Over the next three years, 25 people develop the disease.

a. What is the prevalence of the disease (per 100) at the beginning of the study? Show work. [3 pts]

P = (75 / 250) * 100 = 30

b. What is the cumulative incidence of the disease (per 100) during the 3 years of follow-up? Show work. [3 pts]

CI = (25 / (250 - 75)) * 100 = 14.29

c. What is the incidence density per 100 person-years? Once again, please show work. [3 pts]

ID = (25 / (175 people * 3 years)) * 100 = 4.76

or, better solution, . . . ID = (25 / ((150 * 3) + (25 * 1.5))) * 100 = 5.13

35. In a population of 10,000, we have 2,000 people over the age of 65 and 250 live births. The total number of deaths is 200 and the number of deaths in people over 65-years of age is 50. Two infants under the age of one die during the year. (In answering these questions, please leave your answer in the form of a fraction.) [2 pts each]

a. Calculate the crude birth rate.

250 / 10,000

b. Calculate the crude death rate.

200 / 10,000

c. Calculate the age-specific death rate for those over 65-years of age.

50 / 2000

d. Calculate the infant mortality rate.

2 / 250