Epidemiology week 1

Question 1

Understand the scientific basis for clinical medicine

Answer 1

Answers to any clinical question requires measurement and hypothesis testing

Question 2

Define biostatistics (understand importance of)

Answer 2

statistics applied to analysis of biological data

Question 3

Define epidemiology (understand importance of)

Answer 3

study of disease ocurrence in human populations, with application to control of health problems

Question 4

Define evidence-based medicine (EMB)

Answer 4

application of clinical epidemiology to the care of patients, or conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients

Question 5

Understand sampling of populations

Answer 5

using a limited portion of a population to make inferences about the larger population as a whole

Question 6

Understand role of bias/chance

Answer 6

chance is a random error that can limit the reliability of evidence given. Bias is a systemic error that limits the accuracy of evidence given.

Question 7

Understand internal validity

Answer 7

degree to which results of a study are correct for the sample of patients being studied

Question 8

Understand external validity

Answer 8

degree to which results of an observation hold true in other settings

Question 9

Understand generalizability of medical information

Answer 9

expresses the validity of assuming that patients in a study are similar to other patients

Question 10

Define incidence

Answer 10

number of new cases of disease that occur during a specified period of time in a population at risk for developing the disease. Is a measure of risk

Question 11

Define prevalence

Answer 11

number of existing cases of disease at a specific point in time or during a specified period of time. = number of cases of disease/number in population at a specified point in time

Question 12

Relationship of duration of disease with incidence and prevalence

Answer 12

Average duration of disease = prevalence/incidence

Question 13

Define case-fatality

Answer 13

total number of deaths from specific disease/total number of people with the disease

Question 14

Define infant-mortality

Answer 14

number of deaths of infants under 1 year of age/live births

Question 15

live birth rate

Answer 15

total number of live births/women of childbearing age

Question 16

crude death (mortality) rate

Answer 16

total number of deaths from all causes/number of people

Question 17

cause-specific death (mortality) rate

Answer 17

total numbers of deaths from a specific disease/number of people

Question 18

incidence density

Answer 18

number of new cases of disease/person-time of observation in candidate population. Expressed as incidents per person-year

Question 19

A survey identified 1,000 cases of a particular disease in a city of 2 million persons in January 2010. One hundred cases were diagnosed during 2010, and 10 cases died during 2010. Assume that all of the new diagnoses occurred before any of the deaths. What is the prevalence of the disease in this city in January 2011?a. 0.5 per 100,000b. 5 per 100,000c. 55 per 100,000d. 50 per 100,000e. 9 per 1,000

Answer 19

C For prevalence, the numerator = number of existing cases in January 2011 = 1,000 cases in January 2010 + 100 incident cases during 2010 – 10 deaths during 2010 = 1,090. Denominator = 2010 population = 2million. (1,090 / 2,000,000) x 100,000 = 54.5 per 100,000 population. Round to the nearest integer.

Question 20

A survey identified 1,000 cases of a particular disease in a city of 2 million persons in January 2010. One hundred cases were diagnosed during 2010, and 10 cases died during 2010. Assume that all of the new diagnoses occurred before any of the deaths. What is the cumulative incidence of the disease in this city in 2010? a. 0.5 per 100,000b. 5 per 100,000c. 55 per 100,000d. 50 per 100,000e. 9 per 1,000

Answer 20

BFor cumulative incidence, the numerator = new cases in 2010 = 100. Denominator = people at risk of disease in January 2010 = 2 million residents – 1,000 who are not at risk because they already have the disease = = 1,999,000. Cumulative incidence = (100 / 1,999,000) x 100,000 = 5 per 100,000 population.

Question 21

A survey identified 1,000 cases of a particular disease in a city of 2 million persons in January 2010. One hundred cases were diagnosed during 2010, and 10 cases died during 2010. Assume that all of the new diagnoses occurred before any of the deaths. What is the case-fatality rate of the disease in this city in 2010? a. 0.5 per 100,000b. 5 per 100,000c. 55 per 100,000d. 50 per 100,000e. 9 per 1,000

Answer 21

EFor case-fatality rate, the numerator is the number who died of the disease = 10, and the denominator is the number with the disease = 1,000 existing cases in January 2010 + 100 incident cases. Case-fatality rate = 10/1,100 = .009, or per 1,000 cases of disease.

Question 22

A survey identified 1,000 cases of a particular disease in a city of 2 million persons in January 2010. One hundred cases were diagnosed during 2010, and 10 cases died during 2010. Assume that all of the new diagnoses occurred before any of the deaths. What is the cause-specific mortality rate for this disease in this city in 2010? a. 0.5 per 100,000b. 5 per 100,000c. 55 per 100,000d. 50 per 100,000e. 9 per 1,000

Answer 22

AFor the cause-specific mortality rate, the numerator is the number who died of the disease = 10, and the denominator is the population =2 million.Cause-specific mortality is (10/2,000,000) x 100,000 = .5 deaths per 100,000 (perhaps better reported as 5 deaths per million population).

Question 23

A high rate of ventilator-­‐associated pneumonia (VAP) has been observed among combat casualties since the onset of military operations in Iraq and Afghanistan. During one study, 475 patients were admitted to the ICU for a total of 757 ventilator days. 25 patients were diagnosed with VAP. What is the incidence of VAP per 1,000 ventilator days (rounded to the nearest integer)?a. 61 per 1,000 ventilator days b. 53 per 1,000 ventilator days c. 33 per 1,000 ventilator days d. 21 per 1,000 ventilator days

Answer 23

C For the incidence rate, the numerator is the number of new cases = 25, and the denominator is person-­‐time, reported as the number of ventilator days = 757. Incidence rate = (25/757) x 1,000 = 33 per 1000 ventilator days.

Question 24

Which of the following is an example of incidence rate?a. the number of newly diagnosed breast cancer cases diagnosed during 200 person-­‐years of follow-­‐upb. the number of men who were found to have high blood pressure at their yearly physical examc. the percentage of infants born with spina bifida (a type of birth defect) among 1,000 liveborn infantsd. the number of drivers found to be using their cell phones at the time of the car accidentamong 1,000 car accidents

Answer 24

A In response A, the numerator includes only new cases, and the denominator is measured in person-­‐ time, so this is an incidence rate (rather than cumulative incidence). B and D measure prevalence because they focus on existing cases at a specific point in time, C is incidence because it involves new cases, but it is cumulative incidence rather than an incidence rate because the denominator is population (births) not person-­‐time.

Question 25

If the incidence rate of a particular disease is 25/100,000 person-­‐years and the prevalence of this disease in the population is 75/100,000, what is the average survival time of individuals who contract this disease?a. 1 year b. 3 yearsc. 3 months d. 4 months

Answer 25

B In a steady state, prevalence = incidence x duration and duration = prevalence/incidence = (75 per100,000 population) / (25 per 100,000 population per year) = 3 years

Question 26

A researcher wants to know whether age confounds the association between history of smoking and coronary heart disease (CHD). Which of the following must be true for age to be a confounder?a. Age is associated with CHDb. Age is associated with history of smoking c. Age is not caused by history of smokingd. B and Ce. A, B and C

Answer 26

E A confounder must be associated with both the exposure and the outcome, but cannot be caused by the exposure.

Question 27

In a study of the association between sudden infant death syndrome (SIDS) and infant sleep habits, parents of infants who died of SIDS were interviewed by the medical examiner after the infant’s death, and a comparison group of parents of living infants was asked to fill out a questionnaire about their infant’s typical sleep habits. Differences in infant sleep habits between the two groups could be due to which of the following: a. Selection biasb. Measurement bias c. Confoundingd. Random errore. External validity (generalizability)

Answer 27

B The key information (infant sleep habits) was measured differently in the two groups. Any differences between the two groups could be because the medical examiner was more aggressive in obtaining information, or because the parents of the SIDS infants tried harder to recall the information, and not necessarily because the sleep habits under investigation caused SIDS.

Question 28

Hormone replacement therapy (HRT) was shown to be associated with lower risk of coronary heart disease (CHD) in several observational studies. One possible explanation is that women who were more health-­‐conscious in general were both more likely to take HRT and more likely to take other measures to prevent CHD. This is an example of:a. Selection biasb. Measurement bias c. Confoundingd. Random errore. External validity (generalizability)

Answer 28

C If health consciousness is associated with HRT use and with lower risk of CHD, but is not caused byHRT use, it could confound the association between HRT and CHD.

Question 29

A study has established the effectiveness of a new treatment for high blood pressure in adults age40-­‐65. Your patient is 83 years old. The primary problem with using the results of this study when deciding on treatment for your patient is:a. Selection biasb. Measurement bias c. Chanced. Confoundinge. External validity (generalizability)

Answer 29

E The results of the study may be internally valid, in that they yield correct results for the sample in which the study was conducted, but that sample is different from your patient, so the results cannot necessarily be generalized to your patient.

Question 30

In a study of psychiatric problems among veterans of OIF and OEF, all psychiatric conditions except post-­‐traumatic stress disorder occurred at a lower rate in combat-­‐deployed personnel than in personnel who were not deployed to a combat zone. This likely reflects the fact that only those persons who have proven their resilience during training remain eligible for combat. If the original goal of the study was to examine the effects of combat on mental health, this finding is an example of:a. Selection biasb. Measurement bias c. Confoundingd. Random errore. External validity (generalizability)

Answer 30

A The two groups (combat-­‐deployed and non-­‐deployed) differ with respect to resilience.

Question 31

Which type of measure of disease frequency best describes the following: the percentage of healthy, at-­‐risk children in a daycare who develop impetigo (a skin disease) during March 2011?a. Prevalenceb. Incidence densityc. Incidenced. None of the above

Answer 31

C Incidence (also known as “cumulative incidence”). Numerator is new cases (children who develop impetigo), and denominator is persons at risk (“healthy, at-­‐risk children”) during a particular time period (March 2011).

Question 32

Which measure of disease frequency best describes the following: the percentage of nursing home residents who have bed sores on July 1, 2010?a. Prevalence b. Incidencec. Incidence density d. None of the above

Answer 32

A Prevalence: Numerator is existing cases at a particular point in time, and denominator is the population of nursing home residents.

Question 33

Which measure of disease frequency best describes the following: the number of healthy, at risk women in the Black Women’s Health Study who develop hypertension during 121,600 person-­‐years of follow-­‐up.a. Prevalenceb. Incidencec. Incidence density d. None of the above

Answer 33

C Incidence density: Numerator is new cases and denominator is person-­‐years of follow-­‐up.