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BMS1. EBM > Lecture 5 and 7 (Study Types) > Flashcards

Lecture 5 and 7 (Study Types) Flashcards

1
Q

Cohort study definition:

A
  • prospective, observational.
  • start with no diseases, look at exposure and disease development over time.
  • more expensive than case-control.
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2
Q

Statistic utilized for cohort study:

A

RELATIVE RISK

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3
Q

Cross-sectional study definition:

A
  • single time point, observational.
    • take a slice of the population
  • how many people have a disease or a risk factor right now
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4
Q

Statistic for cross-sectional study:

A

POINT PREVALENCE

point prevalence = (total #sick)/(total population)

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5
Q

Case-control study definition:

A
  • retrospective, observational.
  • start with disease and go back retrospectively to find the risk factor
  • cheaper than cohort studies
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6
Q

Statistic for case-control study:

A

ODDS RATIO

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7
Q

Nested case-control study definition:

A
  • select cases and controls from a cohort study
  • go back and find the risk factor
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8
Q

The three types of error in studies:

A
  1. random (chance)
  2. systematic (bias)
  3. confounders
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9
Q

Random error:

A
  • chance
  • will cancel out as sample gets larger
  • more likely will lead to type 2 error
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10
Q

Systematic error (bias):

A
  • cannot be corrected for regardless of sample size
  • more likely will lead to a type 1 error
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11
Q

Confounder definition:

A
  • must be associated with exposure
  • must be associated with outcome
  • cannot be in the causal pathway between exposure and outcome
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12
Q

How can you control for confounding?

A
  • At the design stage:
    • randomization
    • restriction
    • matching
  • At the analysis stage:
    • stratification
    • multivariable adjustment (regression)
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13
Q

Selection bias:

A
  • nonrandom assignment to groups
  • loss to follow up
  • must be controlled at design stage.
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14
Q

Healthy worker effect (bias):

A
  • workers are generally healthier than the general population.
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15
Q

Self-selection bias:

A
  • research volunteers different from the general population in terms of their exposure and disease status.
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16
Q

Withdrawal bias:

A
  • differential loss to follow-up; people drop out
  • drop outs may be more sick
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17
Q

Recall bias:

A
  • knowledge of presence of disease changes subject’s response
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18
Q

Sampling bias:

A
  • subjects are not representative of population, non-generalizable
19
Q

Confounding bias:

A
  • one factor distorts/confuses the effect of another closely related one.
20
Q

Information/observer bias:

A
  • researcher’s decision affected by prior knowledge of subject’s exposure.
  • Correct for by blinding.
  • must be controlled at design stage
21
Q

What forms of bias are case-control studies sensitive to?

A
  • recall bias
  • selection bias
  • observer bias
22
Q

Case-control study benefits:

A
  • good for rare diseases
  • can test for a wide variety of exposures
  • important in understanding new diseases
  • commonly used in outbreak investigations
23
Q

Cohort study benefits:

A
  • can choose all the variables you want
  • can control for bias and confounders
24
Q

How to choose sample for case-control study:

A
  • Case definition should not be too broad - misclassifies
  • Case definition should not be too narrow - reduces sample size
  • Cases and controls should be members of the same base population and have had equal opportunity to have been exposed (same environment).
25
Q

Proces of the development and testing of a new clinical test (index test):

A

need to compare index test to reference test:

  1. select patients
  2. test all patients with index test
  3. test and diagnose all patients with reference test
  4. compare index test results with reference test results
26
Q

Potential bias in an index test study:

A
  1. utilization of wrong reference test
  2. spectrum bias
  3. verification bias
  4. observer bias
27
Q

Spectrum bias:

A
  • applies to index test studies
  • patients in study not the same as those found in standard practice
    • i.e. using only patients more likely to test positive - will make test look better
28
Q

Verification bias:

A
  • applies to index test studies
  • not all patients in study receive both the index and reference test
29
Q

Analytical observational studies:

A
  • Observe events as they happen in the ‘real world’ without playing an active role in what happens.
  • “Incidence” studies
  • Two-types:
    1. cohort
    2. case-control
30
Q

What is a cohort?

A
  • a group of people with something in common who are then followed over time to see what happens to them.
    • should not have the outcome at enrollment, but should be at risk for it
31
Q

Effect modifiers are:

A
  • Effect modifiers are variables that change the effect of the exposure of interest on risk of disease.
  • “interaction”
32
Q

Randomization:

A
  • an attempt to evenly distribute potential (unknown) confounders in study groups.
33
Q

Restriction:

A
  • excludes participants with known confounding variables
  • may decrease sample size and power
34
Q

Stratification:

A
  • stratify data by a potential confounder, and then compare both groups
35
Q

Matching:

A
  • For each subject in the exposed group, one or more patients with the same characteristic (with or without the confounder, eg. smoker or nonsmoker) is chosen for the non-exposed group.
  • has to be coupled with a matched analysis
36
Q

Randomized control trial:

A
  • prospective, interventional, gold standard
  • treatment versus placebo — watch outcome
  • statistics: NNT/NNH; multiple comparisons
  • four phases
37
Q

Meta-analysis study:

A
  • retrospective, chart review, platinum standard
  • pools data from multiple studies, usually RCTs
  • analyzes cumulative data to determine external validity
38
Q

Twin concordance study:

A

genes versus environment (early life)

  • monozygotic = identical twin, same genetic material, same environment
  • dyzygotic = non-identical twins, different genetic material, same environment
39
Q

Adoption study:

A

genes versus environment (later life)

  • come from genetically sick family, raised in completely different environment, but still get sick. Hints to powerful effect of genes.
40
Q

RCT Phase 1:

A

SAFETY

  • small # healthy volunteers
  • toxicity
  • pharmacokinetics
    • in cancer, phase I studies will include critically ill/terminally ill patients
41
Q

RCT Phase 2:

A

EFFICACY

  • small # patients with disease
  • dosing
  • adverse reactions
42
Q

RCT Phase 3:

A

TREATMENT VERSUS CONTROL

  • large # patients with disease
  • compares standard treatment to novel treatment
43
Q

RCT Phase 4:

A

post-marketing SURVEILLANCE

  • after drug has been approved
  • watches for rare, long term effects

BMS1. EBM (11 decks)

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