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cohort studies Flashcards

(61 cards)

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1
Q

start with

cohort studies

A

environmental exposure
then find association with disease or outcome

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2
Q

temporality

A

timing of info about cause and effect
we want info about cause and effect gathered at the same time

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3
Q

which studies have no temporality

A

observational studies:
cohort
cross-sectional
case-control

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4
Q

which studies have temporality

A

randomized controlled trial

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5
Q

limits of cross-sectional studies

A

hard to distinguish exposures and outcomes

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6
Q

limits of case-control studies

A

case’s recall of past exposures may be different than that of controls

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7
Q

start with

cohort studies

A

exposed and not exposed group (neither group can have disease)
folow up and categorize by disease or no disease

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8
Q

2 observation points

cohort studies

A
  1. determine exposure status and eligibility
  2. determine incident (new cases
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9
Q

variable of interest

cohort studies

A

incidence
we can find risk!

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10
Q

exposure-based cohort studies are good for

cohort studies

A

rare exposures
occupational groups may have more exposure to certain things
compare to non-exposed group of similar demographics

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11
Q

are cohort studies randomized?

A

no!

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12
Q

no randomization means

A

unclear whether exposure caused disease
or whether a confounder is involved

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13
Q

prospective cohort study

cohort studies

A

start with exposure status in present disease free population, then follow forward to future

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14
Q

retrospective cohort study

cohort studies

A

start with exposure status from past and track forward to present
follow-up has already taken place
reconstructed from records

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15
Q

prospective cohort pros

cohort studies

A
  • exposure assessed before disease occurs
  • can get incidence rate, cum. incidence, RR
  • can study several outcomes to 1 cause
  • NO RECALL BIAS
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16
Q

prospective cohort cons

cohort studies

A
  • slow, expensive
  • large samples (unless risk period is long: since we look at person-years)
  • loss to follow-up
  • not for rare disease
  • not easy to reproduce
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17
Q

retrospective cohort pros

cohort studies

A

rare exposures
cheaper
occupational studies or rare events
may be quick

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18
Q

retrospective cohort cons

cohort studies

A

bad for rare disease
hard to get outcome
hard to get exposure
need to determine duration and intensity of exposure

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19
Q

combined retro and pro cohort

cohort studies

A

exposure from past objective records, may gather more info overtime and follow forward into future

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20
Q

design: assembling the cohort

cohort studies

A

all must be at risk
exclude ppl with history
maybe limit to higher risk (certain age group)
collab with other areas to increase sample size and generalizability

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21
Q

determine exposure status

cohort studies

A

questionnaires
lab tests
physical measurements
special procedures
hawthrone effect

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22
Q

hawthorne effect

cohort studies

A

be careful about asking about diet every visit, they may begin to eat differently
study begins to influence behaviors

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23
Q

measurement of exposures

cohort studies

A

must be comparable for exposed and unexposed
performed by someone blinded to exposure
examine at predetermined intervals
establish diagnostic critera BEFORE study begins

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24
Q

incidence in exposed

cohort studies

A

a/a+b

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25
incidence in non-exposed | cohort studies
c/c+d
26
cumulative incidence | cohort studies
avg probability an individual in the cohort will develop disease over follow-up period cum incidence = all incident cases over follow-up / all ppl at risk at baseline
27
when should we not use cumulative incidence? | cohort studies
when we lose a lot of people to follow-up
28
incidence rate | cohort studies
incidence rate = all incident cases over follow-up / person-years
29
measures of association | cohort studies
relative risk rate ratio attributable risk
30
relative risk | cohort studies
cum incidence in exposed / cum incidence in nonexposed
31
relative risk = 3 means | cohort studies
disease in exposed is 3 times that in unexposed
32
rate ratio | cohort studies
incidence in exposed / incidence in nonexposed
33
RR = | cohort studies
(a/a+b) / (c/c+d)
34
RR < 1 | cohort studies
risk in exposed < risk in nonexposed neg association may be protective
35
RR = 1 | cohort studies
no association, no risk
36
RR > 1 | cohort studies
risk in exposed > risk in nonexposed pos association may be causal
37
attributable risk aka | cohort studies
risk difference
38
attributable risk | cohort studies
cum incidence exposed - cum incidence in nonexposed shows total increase in incidence
39
absolute measures
greater public health importance bc they tell us incidence and risk difference
40
relative measures
determine causality how strong association is
41
study population
actual study members
42
target population
population you want to generalize your results to
43
generalizability aka
external validity
44
good generalizability =
can generalize results to other populations
45
internal validity
is association btwn exposure and disease a good estimate of real life
46
what is internal validity impacted by
confounding, bias, chance
47
exchangeability
even distribution of confounders unexposed and exposed should be same aside from exposure lower exchangeability = more confounders
48
confounding issue in cohort studies
subjects choose their exposure also smoking
49
other bias in cohort studies
outcome ascertainment bias
50
outcome ascertainment bias | cohort studies
no blinding so clinician may be influenced
51
information bias
quality of info obtained from each group must be equal hard with retrospective
52
loss to follow up
we hope loss from all groups is equal
53
if loss to followup from group a is greater,
relationship is underestimated
54
if loss to followup from group c is greater,
relationship is overestimated
55
unequal loss leads to
bias of RR and AR
56
analytic bias
investigators and statisticians have preconceptions about findings
57
dangers of big sample size
more likely to see association even if it doesn't exist
58
power
probability of finding a statistically significant association in data, given that association exists in population
59
survival analysis
product limit analysis
60
product limit analysis
1 - probability of not developing disease in any time interval
61
product limit analysis = 0.395
in absence of withdrawal, death, loss to followup, 39.5% of cohort would develop disease by time t

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