Unit 2 Flashcards Preview

Epidemiology > Unit 2 > Flashcards

Flashcards in Unit 2 Deck (102):
1

What are the two types of study designs?

descriptive, explanatory

2

Intended to describe a disease condition - signs, lesions, outcomes, occurrence of microbes, etc.

Descriptive study

3

Seeks to identify causes. Has a hypothesis, has controls. Used to investigate a treatment, intervention, or risk factor, in hopes of providing causal evidence.

Explanatory (or causal) study

4

List the two main types of explanatory studies:

experimental, observational (epidemiologic)

5

List the three types of observational studies:

cohort
case control
cross sectional

6

Planned comparison between 2 groups - one receiving one treatment, another receiving a different tx for a naturally disease - researcher has some control

Experimental - Clinical trials

7

Researcher has the greatest control and involves the use of experimental animals. This type of study is the best design to prove cause or demonstrate efficacy

Experimental - laboratory

8

Sometimes called "natural studies" as they occur freely in nature.

Observational studies

9

Why are observational studies under the category of "explanatory type" studies?

the goal is to assess cause

10

What is the difference between observational and experimental studies?

Which animals go to treatment groups is not under control of the researcher for observational

11

Observational studies contribute to the body of evidence implicating a ______ as a cause. They often do not provide sufficient ________, in one study, to establish a cause.

factor; evidence

12

a group sharing a defining characteristic

cohort

13

Type of observational study that is prospective in time:

cohort

14

What are the two types of cohorts featured in a study?

1. one exposed to a factor
2. one NOT exposed to a factor

15

Subjects are followed in time, and incidence of one or more diseases are compared between the two groups:

cohort

16

For a cohort study, what does a relative risk >1 indicate?

an increased risk in exposed, compared to unexposed

17

For a cohort study, what does a relative risk =1 indicate?

that the risk in exposed is the same as the risk in the unexposed

18

For a cohort study, what does a relative risk <1 indicate?

that the disease in the exposed is less than the unexposed

19

A relative risk < 1 for a cohort study indicates that exposure has a "sparing effect". What does this mean?

a reduction in risk associated with exposure

20

What kind of exposures might give a sparing effect?

vaccinations

21

Measure of the strength of association between a factor and a disease:

relative risk

22

Relative risk can ONLY be calculated in what 2 studies?

cohort and cross-sectional

23

Cannot be estimated in a case-control study:

relative risk

24

What is the equation for relative risk?

(proportion with disease in exposed)/(proportion with disease in unexposed)

25

Well suited for studying disease and exposures that occur relatively commonly:

cohort

26

Well suited to study the effect of multiple outcomes following a single exposure:

cohort

27

What are two benefits of cohort studies?

1. researcher has control over data quality (recorded in real time)
2. time sequence of "cause" and disease is clear

28

Factor A occurs before disease X

temporal relationship

29

Factor A is present very often in cases, and not in controls:

strength of association

30

The more factor A you have, the greater the disease chance

dose-response relationship

31

Based on what is known, Factor A could cause disease X

biological plausibility

32

The relationship between Factor A and disease X is seen repeatedly, time and again

Consistency of multiple studies

33

Other causes are not likely or impossible

rule out other possible causes

34

Removal of Factor A results in diminished disease

reversible association

35

A selected group within the population is sampled once and exposure and disease are simultaneously measured:

cross sectional (prevalence) study

36

How are cross sectional studies not like cohort studies?

animals are NOT followed in time to establish disease incidence

37

What are the advantages of cross-sectional studies?

- short, fast, inexpensive
- can gather data on multiple diseases/exposures
- provides preliminary evidence for further study

38

Cohort studies are usually conducted in a:

prospective manner

39

Animals with a disease

"cases"

40

Animals without disease:

"comparands"

41

Study in which animals with a disease are compared with one more controls:

case-control

42

Can be used to study rare (infrequent) disease:

case-control

43

Why are case-controls considered retrospective studies?

look into the past and compare the frequency of occurrence of risk factors for cases vs. controls

44

Odds of exposure in cases compared to odds of exposure in non-cases

odds ratio

45

What two measurements assess the strength of association between exposure and disease (but in slightly different ways)?

1. relative risk (cohort)
2. odds ratio (case-control)

46

The probability of an event occurring to the probability of the event not occurring:

odds

47

Which measure of association can be used in case-control AND cohort studies?

odds ratio (RR is easier for cohort though)

48

When are OR and RR pretty close?

when the disease is rare (<10%)

49

How to calculate OR =

(ad)/(bc)

50

An odds ratio > 1 indicates:

an increased risk

51

An odds ratio = 1 indicates:

there is no increased risk

52

An odds ratio < 1 indicates:

a "sparing" effect

53

estimates risk of exposure in cases, compared to exposure in controls:

OR (case-control)

54

estimates risk of disease in exposed, compared to risk of disease in non-exposed:

RR (cohort)

55

A population of animals is sampled at a specific point in time:

cross-sectional

56

How is each animal classified in a cross sectional study?

according to status of outcome and risk factor, simultaneously, at the time of the snapshot

57

Can be used to assess absolute risks in the population

cross-sectional

58

Typically refers to the assessment of serum antibody concentration:

serology

59

The point at which we have diluted a serum sample and measured until there is no longer a reaction:

"end point titer"

60

What is the idea behind testing serology?

you can determine the last dilution at which an Ag:Ab reaction occurs (end point titer)

61

What does seropositivity depend on for each titer?

cut-off point

62

You must be over the critical titer to be classified as:

positive

63

A 2 fold increase (or 1 dilution) between week 1 and week 4 is considered:

laboratory error

64

A four fold increase (or 2 diluations) between week 1 and week 4 is considered:

to be greater than lab error, reflecting active Ig production

65

Why do we often use the Log2 transformation when talking titers?

much easier to work with when they assume a normal distribution

66

Ability to correctly classify (detect) disease animals. Expressed as a proportion:

sensitivity

67

The test that is used to determine if a disease is truly present or not. Other tests are compared to it to determine their "accuracy"

gold standard

68

Of those truly D+, the proportion correctly classified by Test Z

Sensitivity

69

Ability of a test to correctly detect (classify) non-diseased animals.

Epidemiologic specificity

70

The ability to measure the correct substance (i.e. not measuring particles or molecules other than the target):

analytical specificity

71

how close a test result is to the truth

accuracy

72

What may be different if comparing populations in early vs. late stages of disease?

sensitivity

73

Properties of the test that allow for comparison between tests (i.e. 2 test for detection of FeLV):

sensitivity, specificity

74

Higher sensitivity improves _____ and helps identify the disease. It rules ____ disease.

NPV; OUT (SnOUT)

75

How does lower specificity alter PPV?

decreases it

76

Lower specificity =

more false positives

77

A more sensitive test reduces _______ ________ and increases NPV.

false negatives

78

SnOUT -

helps rule out disease

79

A more specific test reduces _____ __________ and improves PPV.

false positives

80

SpIN -

rules in disease

81

By altering the cutpoint, you alter:

sensitivity and specificity

82

Increased sensitivity results in:

lower specificity, fewer false negatives, more false positives

83

When is it advantageous to alter the cut-off point in a test?

if you want to rule in/out a disease

84

Two or more tests are conducted sequentially based on the results of a previous test:

serial testing

85

In serial testing, only animals that test ________ to the first test are tested again.

positive

86

In serial testing, only animals that are positive on __________ are considered positive.

all tests

87

Used for diagnosis when time is not crucial or if diagnosing a patient when disease positive has a grave outcome.

Serial testing

88

Conduction two or more tests on a patient at the same time:

parallel testing

89

If any one test is positive, the animal is categorized as sick:

parallel testing

90

When is parallel testing used?

rapid assessment/medical emergencies

91

Increased sensitivity -->

fewer false negatives

92

decreased specificity -->

more false positives

93

Because sensitivity is reduced, you will allow more diseased animals to remain in the herd:

serial testing

94

Relatively small number of positive tests. The pool of positive tests is nearly all “Sick”. But not all sick are in the test + pool.

serial testing

95

Positive test identifies animal at high probability of Illness,
Confidence in Positives SpIN

serial testing

96

More positive tests. Positive pool captures almost all ill, but includes many non-ill too.

parallel testing

97

The negative test pool ID's "well" animals. Confidence in Negatives SnOUT

parallel testing

98

single numbers (points) derived from a sample

point estimate

99

represents our best estimate of the true value of the population parameter:

point estimate

100

a range of values that the point estimate could reasonably take

confidence intervals

101

The probability of obtaining the observed value (or more extreme value) when the null hypothesis is TRUE

P value

102

Typically states that there is no difference between the group being compared:

H0 (null hypothesis)