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Block A - Molecules to Global Health COPY > Epidemiology > Flashcards

Epidemiology Flashcards

1
Q

List the basic types of Epidemiologic studies

A
  1. Descriptive epidemiology (distribution, description)

2. Analytical epidemiology (hypothesized causal relationship, evaluating interventions, risk factors)

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2
Q

Recognize primary health outcomes (“the five D’s”)

A 
Death
Disease
Discomfort
Disability
Dissatisfaction

** can add destitution (financial cost of illness)

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3
Q

prevalence

A

proportion of person in population who have the disease at a specific point
= number of existing cases of a disease / total population (at a given time)

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4
Q

describe sensitivity

A

Sensitivity (ability of a test to correctly identify those with the disease, aka true positive rate)
= True positives/(True positives + false negatives)

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5
Q

What are the major biases that complicate the interpretation of studies of screening results.

A
  1. VOLUNTEERISM: people who attend screening differ from those who don’t. The benefits of screening will exaggerate the benefits.
  2. LEAD TIME BIAIS: in evaluating the benefit of screening on reducing mortality, a bias in the comparison of survival tomes may result if lead time is not taken into account. In a RCT, we have to compare mortality, nor survival.
  3. LENGHT -TIME BIAIS: Screening will more likely detect those persons having a longer preclinical disease phase resulting in over representation of slowly progressing disease
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6
Q

however something is measured, we want the mesurement to be…

A
  • Validity: does a measurement reflect the truth? (FREE OF BIAS)
  • Reliability: precision, reproducibility
  • Responsiveness: does it change as the phenomenon changes?
  • Interpretable: Do people reading it know what it means?
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7
Q

Incidence

A

number of NEW events in a population of individuals AT RISK during interval

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8
Q

what are the 2 specific types of incidence mesures ?

A
  1. cumulative incidence

2. incidence rate (incidence density)

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9
Q

cumulative incidence

A

the proportion of individuals INITIALLY FREE of the disease of interest who develop the outcome during a defined time period
CI = # of new cases during a given period/total population at risk

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10
Q

Incidence rate

A

number of events divided by the amount of person-time observed, measures how quickly people are developing the disease
DI = # of new cases of a disease in a given period of time/total person-time of observation

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11
Q

what’s the link between prevalence, incidence and duration ?

A

prevalence = incidence x duration

  • lower prevalence = high incidence, short duration (people who have the disease die fast)
  • higher prevalence = low incidence/long duration (people live with the disease for a long time)
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12
Q

name 2 special types of incidence mesures and why they’re used

A
  • mortality rate

- attack rate (a type of cumulative incidence , for accute epidemis)

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13
Q

why is prevalence mesure useful ?

A
  • most useful for health care providers
  • to assess the public health impact of a specific disease within a community
  • to project medical care needs for affected individuals
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14
Q

why is incidence mesure useful ?

A
  • assessing exposure disease relationship

- risk factors for disease

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15
Q

what are adjusted rates ?

A

used to be able to compare rates between two populations that are different in terms of some important characteristics (age structure, sex, etc.)

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16
Q

what would be the best Dx test ?

A
  • valid
  • reliable
  • inexpensive
  • easy to administer
  • of minimal discomfort to the patient
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17
Q

what are the most useful test in clinical practice ?

A

those who produce the biggest changes from pretest to post-test probabilities

18
Q

specificity

A

ability of the test to correctly identify those without the disease, aka true negative rate
= true negative / (true negative + false positive)

19
Q

predictive value of a positive test (PPV)

A

probability that subjects with a positive screening test truly have the disease
= true positive / (true positive + false positive)

20
Q

predictive value of a negative test (NPV)

A

probability that subjects with a negative screening test truly don’t have the disease
= true negative / (true negatives + false negatives)

21
Q

do sensitivity and specificity change with prevalence ?

A

No, these remain fixed characteristics independant of what population the test is performed/disease prevalence

22
Q

on what depend PPV and NPV ?

A
  • sensitivity
  • specificity
  • prevalence of the disease
23
Q

as prevalence increase, what PPV and NPV increase or decrease ?

A

PPV increase and NPV decrease

24
Q

what are likelihood ratios ?

A
  • a way to incorporate the sensitivity and specificity of a test in a single mesure
  • LIKELIHOOD OF A GIVEN TEST RESULT IN A PERSON WITH THE DISEASE COMPARE TO THE LIKELIHOOD OF THIS SAME RESULT IN A PERSON WITHOUT THE DISEASE
25
Q

LR+

A

Likelihood ratio of a positive test (LR+) if LR+ is 10, the people who have the disease are 10x more likely to test positive
= sensitivity / 1-specificity

26
Q

LR-

A

Likelihood ratio of a negative test (LR-) if LR- = 0.1, people who have the disease are about 0,1 fois more likely to test negative than those who do. (so want it as close to 0 as possible)
= 1-sensitivity / specificity

27
Q

what does high LR+ help to do

A

ruling in the disease = conclusive changes from pre to post-test probabilities

28
Q

what does low LR- value help to do ?

A

RULING OUT the disease

29
Q

a test with a high sensitivity but a low specificity produce

A
  • no false negative

- many false positive

30
Q

a test with a low sensitivity but a high specificity produce

A
  • many false negative

- no false positive

31
Q

how is, for any disease determined the optimal cut-off point ?

A

it has to be selected depending on the consequences of missing a few positive if the cut-off is set higher or of falsely classifying more negatives as positives if the cut-off point is set lower.

32
Q

what’s the receiver operating curve ?

A

a plot of what happens to sensitivity and specificity as different cutoffs are used (for a particular test)

33
Q

what’s the preclinical phase ?

A

the phase between disease onset and symptoms (possible screening)

34
Q

what are the 2 steps of screening ?

A
  1. screening test

2. follow-up for definite diagnosis

35
Q

the feasibility of screening is based on those requirements

A
  1. burden of the disease
  2. availability of effective treatment
  3. performance of test
36
Q

what are the requirement for screening

A
  1. accuracy (high sensitivity and specificity)
  2. reliability (reproducible)
  3. safe and acceptable
  4. simple and inexpensive
37
Q

best trial to compare a screening program ?

A

RCT - randomized control trials

38
Q

what are the negative consequences of screening ?

A
  • physical harm
  • psychological harm
  • false reassurance
  • financial harm
39
Q

what are the disease’s requirements for screening ?

A
  1. severe, common and perceived to be an important population health problem
  2. must be able to significantly alter outcomes such as death or severe disability
  3. significant lead time
40
Q

what are the different types of data ?

A
  • nominal (in categories)
  • ordinal (some sense of order, but interval not specified)
  • interval (inherent order with specified intervals)
41
Q

what are the 3 ways of defining abnormality ?

A
  • abnormal = UNUSUAL
  • abnormal = ASSOCIATED WITH BAD OUTCOME
  • abnormal = TREATABLE (target levels)
42
Q

what’s the regression to the mean ?

A

when you retest someone with an abnormal result, particulary if extreme, the second test will usually come back closer to the mean, for that population

Block A - Molecules to Global Health COPY (8 decks)

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