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FOD > Epidemiology > Flashcards

Epidemiology Flashcards

1
Q

Prevalence

A

Fraction (proportion) of a group of people that have/manifest a clinical condition at a given point in time

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2
Q

Incidence

A

The fraction of a group initially free of disease that develops it over a given period of time

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3
Q

Retrospective

A

Case-control studies are _____

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4
Q

Prospective

A

Cohort studies are ______

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5
Q

Case-control studies

A

Subjects are selected on the basis of whether they do or do not have a particular disease or outcome of interests. Compared for their exposure or risk factor history

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6
Q

Pros of case-control study

A
  • Long latency periods
  • Inexpensive
  • Optimal for evaluation of rare diseases or rare outcome
  • Can examine multiple risk factors for a single disease or outcome
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7
Q

Cons of case-control study

A

Particularly prone to biases and confounding (statisical association but not true cause and effect)
Inefficient for the evaluation of rare EXPOSURES

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8
Q

Selection bias

A

Present when individuals have different probabilities of being included in the study sample according to relevant study characteristics; most often the exposure and outcome of interest

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9
Q

Information bias

A

Results from a systematic tendency for individuals selected for inclusion in the study to be erroneously place in different exposure/outcome categories, thus leading to misclassification

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10
Q

(a/c)/ (b/d) (outcome and exposure/outcome no exposure)/(no outcome and exposure/no outcome and no exposure)

A

Odds ratio, shows strength of association

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11
Q

Odds ratio

A

Means that the ratio of exposure for people with disease to people without is x. Equals relative risk if a rare outcome

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12
Q

Case control questions

A
  1. Was there a pre-specified hypothesis defining a relationship between an exposure and an outcome?
  2. Were the exposure and health outcome clearly and operationally defined?
  3. Was the control group appropriate? (from base population)
  4. Was the measurement of exposure both in cases and controls accurate and unbiased?
  5. Was the measurement of outcome both in casea and controls accurate and unbiased?
  6. Were the important confounding variables accounted for and controlled for in the statistical analysis?
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13
Q

Cohort study

A

Cohort is defined, exposure status is determined, follow prospectively over time, identify development of disease/outcome, compare incidence of disease in two groups

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14
Q

identify cohort in cohort study

A
  1. Select defined population before exposures are identified
    or 2. Create a study populatoin by selecting participants based on exposure

all participants (exposed and un) must be at risk for developing the outcome of interest

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15
Q

Incidence

A

A/ (A +B) or (outcome and exposed)/ all exposed

C/ (C +D) or (outcome and unexposed)/all unexposed

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16
Q

Relative risk

A

Ratio of risk (incidence) of disease in exposed persons to risk in unexposed persons
measure of association

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17
Q

(A/ (A +B)) / (C/(C+D))

A

Relative risk equation

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18
Q

AR = (Incidence Ex - Incidence UnEx)/ Incidence Ex

A

Attributable risk equation

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19
Q

Advantages of cohort studies

A
  • Can determine temporal sequence, identify natural history of disease
  • assessing multiple outcomes after a single exposure
  • identify incidence and RR
  • Reduces or eliminates recall bias
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20
Q

Disadvantages of cohort studies

A
  • Can be inefficient and costly, esp for rare diseases or with long history
  • Attrition/loss to follow up (bias to exposed vs unexposed)
  • Selection bias
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21
Q

Equipoise, efficacy, effectiveness

A

Three E’s of RCT

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22
Q

Randomized Controlled Trials

A

Gold Standard, removes selection bias and benefit seen is less likely to be due to confounding or other biases. More likely a true association

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23
Q

Equipoise

A

Term to describe state of equilibrium in which two sides are balanced. Only ethical to do a RCT is you don’t know which treatment is better

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24
Q

Phase 1

A

Initial human trials, small sample (1-100), healthy volunteers with no comparison group

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25
Q

Evaluate safety (adverse effects, max dose, treatment mechanism)

A

Primary goal of Phase 1 trial

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26
Q

Phase 2

A

Expanded human trials, small sample (100s), patients with disease, comparator group

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27
Q

Expanded safety, efficacy, optimal dosing and duration

A

Goals of Phase 2 trials

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28
Q

Phase 3

A

Randomized Controlled Trial, large sample (100-1000s) with disease and comparator group. Expensive and costly

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29
Q

Determine efficacy and additional info on safety (adverse effects)

A

Primary goal of Phase 3 trial

30
Q

Phase 4

A

After FDA approval, post-market surveillance. Ongoing monitoring in real world setting. Identify additional adverse effects

31
Q

Efficacy

A

The benefit of the intervention under IDEAL conditions

32
Q

Effectiveness

A

The benefit of the intervention in the REAL WORLD setting

33
Q

RCT with placebo comparison, highly select population (strict in/exclusion), intervention is highly standardized

A

Testing for efficacy

34
Q

Comparison to “current standard”, generalizable population, few exclusions, intervention implementation flexible

A

Testing for effectiveness

35
Q

Randomization

A

Eliminates selection bias- removes potential for bias in the allocation of subjects to the treatment groups. On average, makes groups comparable with respect to known and unknown confounders

36
Q

Benefits of randomization are lost

A

Problem with study participants dropping out, switching treatment groups, or failing to comply with assigned treatment

37
Q

Table 1

A

In most research publications, lists baseline characteristics by treatment group

38
Q

RRR (relative risk reduction)

A

Gives percent that intervention is less likely to develop outcome. Can over-inflate benefits or risks, esp for rare outcomes

39
Q

(Risk for control- risk for treatment)/risk for control

A

RRR equation

40
Q

Risk of outcome in control - risk of outcome in treat group

A

Absolute risk reduction (ARR) equation. Says percent fewer who develop outcome

41
Q

1/ARR

A

Number needed to treat (NNT) equation

42
Q

Intention-to-treat

A

Analyze participants who switched treatment groups, didn’t comply, or dropped out-analyze according to original group assignment. Simulates “real world”
“How does treatment work in poeple for whom it was targeted”

43
Q

Per-protocol analysis

A

Analyze participants who switched treatment groups, didn’t comply, or dropped out-analyze depending on what they followed
“How does the treatment work in people who actually received the treatment”

44
Q

Advantages of RCT

A

Eliminates selection bias. Definitive trial if well done

45
Q

Disadvantages of RCT

A

High resource- cost, time, effort

Requires equipoise and may not be ethical

46
Q

Randomized Cluster Trial

A

Experiments in which clusters of participants, rather than single individuals are randomly allocated to intervention groups. When intervention can’t be applied to an individual or there is contamination across individuals

47
Q

Meta-analyses

A

Combines results of RCTs from small studies- essentially creating ONE larger study

48
Q

RR not equal to 1 (cohort) or OR not equal to 1 (case control)

A

Study factor is associated with the study outcome when

49
Q

Statistical ways to adjust for confounding but not to control for bias

A

difference between confounders and bias

50
Q

Criteria for confounding

A

Must differ by levels of exposure variable, must be associated with study outcome

51
Q

Adjust for confounding during study design

A

Restrict (limit ages), match (force balance, match confounding variable), randomly allocate persons to study groups

52
Q

Adjust for confounding after data are collected

A

Stratify (compare old with old, young w young, etc), adjust (combine stratified results into 1 estimate)

53
Q

RR of groups is same, but not the same as overall RR

A

After stratifying on levels of confounders, confounding exists if ____

54
Q

Intermediate variable

A

Variable to be adjusted lies between study factor and outcome, NOT a confounding variable and doesn’t need to be controlled

55
Q

Effect modification

A

RR’s differ importantly across levels of stratification variable. Effect not homogeneous, degree of association depends on level of stratification variable (RR are different between groups)

56
Q

Specificity

A

Ability of a test to correctly identify persons without disease. proportion of persons without disease who have a negative test. only identify disease

57
Q

TN/ (TN + FP)

A

Specificity equation

58
Q

TP/ (TP + FN)

A

Sensitivity equation

59
Q

Sensitivity

A

Ability to identify persons with disease, identify all disease. Proportion of persons with disease with positive test

60
Q

TP/ (TP + FP)

A

PPV

61
Q

TN / (TN+ FN)

A

NPV

62
Q

Predictive values

A

Vary according to population tested

63
Q

Screening test

A

Identifies people at low risk for disease. Maximizes sensitivity. When pts have no symptoms

64
Q

Diagnostic test

A

Determine whom among those at risk actually has disease. Maximizes specificity, few false positives. Done when pt has symptoms

65
Q

Bayes’ Theorem

A

Interpretation of new information depends on what you already know about the patient

66
Q

Overuse

A

Medical care in which harms outweighs benefits, benefits are negligible, or fully informed patients would forego medical care

67
Q

Overdiagnosis

A

Diagnosis of abnormalities not related to disease (false positive), identify disease that will never cause illness

68
Q

Overtreatment

A

Overdiagnosed disease, wrong practice, unwanted care

69
Q

Quasi-experimental study

A

Study that aims to evaluate interventions but does not utilize a randomized control group, frequently utilized in quality improvement

70
Q

Selection bias, historical bias, regression, maturational effects

A

Threats to internal validity in QE studies

FOD (5 decks)

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