Epidemiology

Question 1

what is validity?

Answer 1

accuracy - does it correspond to what is true

Question 2

what is reliability ?

Answer 2

precision - does it give consistent results when repeated

Question 3

(reliability/validity):
1. sensitivity
2. specificity
3. likelihood ratios

Answer 3

all three are part of validity

Question 4

what is the gold standard? (2)

Answer 4

• The method that would ideally give 100% correct results
• Does not exist, we use the best test available

Question 5

what is pre-test probability?

Answer 5

probability of having the disease BEFORE testing

Question 6

what is post-test probability?

Answer 6

probability of disease AFTER test result

Question 7

are the pre-test and post-test probabilities low or high for:
1. a positive test
2. a negative test

Answer 7

1. pre-test: low, post-test: high
2. pre-test: high, post-test: low

Question 8

what is a true positive?

Answer 8

positive test + disease positive

Question 9

what is a false negative?

Answer 9

negative test + disease positive

Question 10

what is a true negative?

Answer 10

negative test + disease negative

Question 10

what is a false positive?

Answer 10

positive test + disease negative

Question 11

what is sensitivity? how do we calculate it?

Answer 11

• true positive rate (positive test +disease positive)
• proportion of patients with disease who test positive
• TP / TP +FN (denominator is everyone who is disease positive, regardless of test result)

Question 12

what is specificity? how do we calculate it?

Answer 12

• true negative rate (negative test + disease negative)
• proportion of patients without the disease who test negative
• TN / TN + FP (denominator is everyone who was disease negative, regardless of test result)

Question 13

what is the predictive value of a positive test? how do we calculate it?

Answer 13

• proportion of patients with positive tests who have the disease
• TP / TP + FP (denominator is people with positive test, regardless of disease presence)

Question 14

what is the predictive value of a negative test? how do we calculate it?

Answer 14

• proportion of patients with negative tests who don’t have the disease
• TN / TN + FN (denominator is people with negative test, regardless of disease presence)

Question 15

T/F: sensitivity and specificity change with prevalence and incidence.

Answer 15

FALSE: they are fixed characteristics

Question 16

T/F: PPV and NPV change with prevalence and incidence.

Answer 16

TRUE

Question 17

As prevalence increases, (increase/decrease)
1. PPV ____
2. NPV ___

Answer 17

1. increase
2. decrease

Question 18

what do we need to consider when determining pretest probability? (3)

Answer 18

• Prevalence of disease
• Characteristics of patient pool
• Info about the patient

Question 19

what is the receiver operating characteristic curve and what do we want it to look like?

Answer 19

• shows what happens to sensitivity and specificity as different cutoffs are being used
• want curve to be closer to 1 (means test is more accurate)

Question 20

what is epidemiology? (2)

Answer 20

1. the study of disease occurrence in human populations
2. the study of distribution and determinants of disease frequency

Question 21

Describe the Grand Experiment (3)

Answer 21

• John Snow thought cholera was reproduced in the body and spread through water/food
• compared 3 districts that had different water companies (randomized)
• statistical association between water company (contamination level) and death from cholera

Question 22

what are the two types of epidemiology?

Answer 22

1. descriptive epidemiology
2. analytical epidemiology

Question 23

what is descriptive epidemiology? (2)

Answer 23

• distribution of disease in population
• description in terms of person, time and place

Question 24

what is analytic epidemiology?

Answer 24

- examine hypothesized causal relationship - identify or measure effect of risk factors or health effect of specific exposure

Question 25

what were the 3 high impact studies in epidemiology?

Answer 25

1. framingham heart study: equations for CVD risk 2. British doctors study: link between smoking and cancer 3. Nurses' health study: risk factors for chronic diseases in women

Question 26

what are the 5 D's (outcomes of disease)?

Answer 26

1. death: bad outcome (mortality) 2. disease (symptoms, signs, abnormalities - morbidity) 3. discomfort 4. disability 5. dissatisfaction

Question 27

what is the 6th destitution?

Answer 27

financial cost of illness (for individuals or society)

Question 28

what are the main epidemiological tools? (6)

Answer 28

1. vital statistics (mortality) 2. disease registries 3. notifiable disease 4. administrative systems 5. special surveillance systems 6. community assessments

Question 29

what is prevalence and how do we calculate it?

Answer 29

- proportion of persons in population who have a disease at a specific time point - cases / total population

Question 30

T/F: point prevalence and prevalence are two different things

Answer 30

FALSE

Question 31

what is incidence?

Answer 31

quantifies nb of new cases of disease that develop in population AT RISK during specified interval

Question 32

what are the two types of incidence measures?

Answer 32

1. cumulative incidence (incidence proportion) 2. incidence rate (incidence density)

Question 33

T/F: when calculating incidence of endometrial cancer (uterus), we include men and women

Answer 33

FALSE: only women are at risk since only they have a uterus!!

Question 34

what is cumulative incidence (incidence proportion)? how do we calculate it?

Answer 34

- proportion of individuals initially free of the disease who develop it during a time period - nb new cases / population at risk

Question 35

T/F: cumulative incidence is the probability or risk of developing a disease

Answer 35

TRUE

Question 36

what is incidence rate (density) and how do we calculate it?

Answer 36

- nb of events divided by the amount of person-time observation - new cases / total person-time of observation

Question 37

T/F: incidence rate measures how quickly people are developing a disease T/F: incidence rate is the TRUE rate because it measures number of cases per unit time

Answer 37

TRUE for both

Question 38

how are prevalence and incidence rate related?

Answer 38

prevalence = incidence rate x duration

Question 39

what are the special types of incidence measures? (2)

Answer 39

1. mortality rate 2. attack rate (cumulative incidence)

Question 40

when are prevalence and incidence most helpful?

Answer 40

- prevalence is most useful for health care providers (assess public health impact) - incidence is most useful to assess exposure disease relationship and risk factors

Question 41

DO SOME PRACTICE QUESTIONS

Answer 41

DO SOME PRACTICE QUESTIONS