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Epidemiology > Unit 2 > Flashcards

Unit 2 Flashcards

1
Q

What are the two types of study designs?

A

descriptive, explanatory

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2
Q

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

A

Descriptive study

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3
Q

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

A

Explanatory (or causal) study

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4
Q

List the two main types of explanatory studies:

A

experimental, observational (epidemiologic)

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5
Q

List the three types of observational studies:

A

cohort
case control
cross sectional

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6
Q

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

A

Experimental - Clinical trials

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7
Q

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

A

Experimental - laboratory

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8
Q

Sometimes called “natural studies” as they occur freely in nature.

A

Observational studies

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9
Q

Why are observational studies under the category of “explanatory type” studies?

A

the goal is to assess cause

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10
Q

What is the difference between observational and experimental studies?

A

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

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11
Q

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.

A

factor; evidence

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12
Q

a group sharing a defining characteristic

A

cohort

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13
Q

Type of observational study that is prospective in time:

A

cohort

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14
Q

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

A
  1. one exposed to a factor

2. one NOT exposed to a factor

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15
Q

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

A

cohort

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16
Q

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

A

an increased risk in exposed, compared to unexposed

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17
Q

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

A

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

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18
Q

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

A

that the disease in the exposed is less than the unexposed

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19
Q

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

A

a reduction in risk associated with exposure

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20
Q

What kind of exposures might give a sparing effect?

A

vaccinations

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21
Q

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

A

relative risk

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22
Q

Relative risk can ONLY be calculated in what 2 studies?

A

cohort and cross-sectional

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23
Q

Cannot be estimated in a case-control study:

A

relative risk

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24
Q

What is the equation for relative risk?

A

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

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25
Q

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

A

cohort

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26
Q

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

A

cohort

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27
Q

What are two benefits of cohort studies?

A
  1. researcher has control over data quality (recorded in real time)
  2. time sequence of “cause” and disease is clear
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28
Q

Factor A occurs before disease X

A

temporal relationship

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29
Q

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

A

strength of association

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30
Q

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

A

dose-response relationship

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31
Q

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

A

biological plausibility

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32
Q

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

A

Consistency of multiple studies

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33
Q

Other causes are not likely or impossible

A

rule out other possible causes

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34
Q

Removal of Factor A results in diminished disease

A

reversible association

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35
Q

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

A

cross sectional (prevalence) study

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36
Q

How are cross sectional studies not like cohort studies?

A

animals are NOT followed in time to establish disease incidence

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37
Q

What are the advantages of cross-sectional studies?

A
  • short, fast, inexpensive
  • can gather data on multiple diseases/exposures
  • provides preliminary evidence for further study
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38
Q

Cohort studies are usually conducted in a:

A

prospective manner

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39
Q

Animals with a disease

A

“cases”

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40
Q

Animals without disease:

A

“comparands”

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41
Q

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

A

case-control

42
Q

Can be used to study rare (infrequent) disease:

A

case-control

43
Q

Why are case-controls considered retrospective studies?

A

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

44
Q

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

A

odds ratio

45
Q

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

A
  1. relative risk (cohort)

2. odds ratio (case-control)

46
Q

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

A

odds

47
Q

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

A

odds ratio (RR is easier for cohort though)

48
Q

When are OR and RR pretty close?

A

when the disease is rare (<10%)

49
Q

How to calculate OR =

A

(ad)/(bc)

50
Q

An odds ratio > 1 indicates:

A

an increased risk

51
Q

An odds ratio = 1 indicates:

A

there is no increased risk

52
Q

An odds ratio < 1 indicates:

A

a “sparing” effect

53
Q

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

A

OR (case-control)

54
Q

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

A

RR (cohort)

55
Q

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

A

cross-sectional

56
Q

How is each animal classified in a cross sectional study?

A

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

57
Q

Can be used to assess absolute risks in the population

A

cross-sectional

58
Q

Typically refers to the assessment of serum antibody concentration:

A

serology

59
Q

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

A

“end point titer”

60
Q

What is the idea behind testing serology?

A

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

61
Q

What does seropositivity depend on for each titer?

A

cut-off point

62
Q

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

A

positive

63
Q

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

A

laboratory error

64
Q

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

A

to be greater than lab error, reflecting active Ig production

65
Q

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

A

much easier to work with when they assume a normal distribution

66
Q

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

A

sensitivity

67
Q

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”

A

gold standard

68
Q

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

A

Sensitivity

69
Q

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

A

Epidemiologic specificity

70
Q

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

A

analytical specificity

71
Q

how close a test result is to the truth

A

accuracy

72
Q

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

A

sensitivity

73
Q

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

A

sensitivity, specificity

74
Q

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

A

NPV; OUT (SnOUT)

75
Q

How does lower specificity alter PPV?

A

decreases it

76
Q

Lower specificity =

A

more false positives

77
Q

A more sensitive test reduces _______ ________ and increases NPV.

A

false negatives

78
Q

SnOUT -

A

helps rule out disease

79
Q

A more specific test reduces _____ __________ and improves PPV.

A

false positives

80
Q

SpIN -

A

rules in disease

81
Q

By altering the cutpoint, you alter:

A

sensitivity and specificity

82
Q

Increased sensitivity results in:

A

lower specificity, fewer false negatives, more false positives

83
Q

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

A

if you want to rule in/out a disease

84
Q

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

A

serial testing

85
Q

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

A

positive

86
Q

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

A

all tests

87
Q

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

A

Serial testing

88
Q

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

A

parallel testing

89
Q

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

A

parallel testing

90
Q

When is parallel testing used?

A

rapid assessment/medical emergencies

91
Q

Increased sensitivity –>

A

fewer false negatives

92
Q

decreased specificity –>

A

more false positives

93
Q

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

A

serial testing

94
Q

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

A

serial testing

95
Q

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

A

serial testing

96
Q

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

A

parallel testing

97
Q

The negative test pool ID’s “well” animals. Confidence in Negatives SnOUT

A

parallel testing

98
Q

single numbers (points) derived from a sample

A

point estimate

99
Q

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

A

point estimate

100
Q

a range of values that the point estimate could reasonably take

A

confidence intervals

101
Q

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

A

P value

102
Q

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

A

H0 (null hypothesis)

Epidemiology (3 decks)

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