Epidemiology

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3 stages in epidemiological research

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descriptive
analytic
experimental

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a typical descriptive study

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survey

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2 typical analytic studies

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cohort
case-control

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3 phenomena assessed in analytic epidemiology

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host
agent
environment

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4 typical host factors

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genetics
behavior
immunological state
age

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numerator for period prevalence

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total cases at beginning + all new cases

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prevalence can be thought of as ___ times ___. an example of this is ___.

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incidence
duration
rise in HIV prevalence after tx became available

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incidence is useful for measuring ___ and assessing ___. it is used in ___ (2) studies

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risk
disease etiology
clinical trials
cohort

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prevalence is useful for ___. it is used in ___ (2) studies.

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planning health services
cross sectional
case-control

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cumulative incidence is ___ divided by ___.

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# of new cases during a time period
population at risk at the beginning

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incidence rate is ___ divided by ___.

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number of new cases observed
total person-time of observation

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3 aims of descriptive epidemiology

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describe natural history of disease
determine allocation of resource
suggest hypotheses about disease causes

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direct age adjustment uses the ___ rates from a specfic population and applies them to the ___ population to obtain a ___ rate.

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age-specific
standard
age-adjusted

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2 kinds of studies

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descriptive
analytical

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2 kinds of analytical studies

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experimental
observational

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3 prospective studies

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clinical trial
cohort
historical prospective

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___ is the most common way to estimate risk

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cumulative incidence

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T/F: at the beginning of a cohort study, some of the cohort has the disease

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false

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the risk measure in a cohort study or ___ is ___. it is the ratio of ___ to ___.

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randomized control trial
relative risk
incidence with exposure
incidence without exposure

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etiology of disease is assessed using risk ratio/difference

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ratio

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T/F: cohort studies are suitable for rare diseases

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false

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5 disadvantages of cohort study

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expensive
large sample needed
takes long time
not suitable for rare diseases
bias due to high dropout rate (loss to follow-up)

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single blinding means

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patient doesn't know whether they're in tx or control

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double blinding means

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patient and person treating them don't know whether pt is in tx or control

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triple blinding means

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pt, person treating them, and data analyst don't know

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number needed to treat (NNT) in terms of absolute risk reduction

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NNT = 1/(ARR)

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in case-control studies, ___ is used to approximate relative risk

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odds ratio

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formula for odds ratio

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OR = (cases exposed*controls not exposed)/(cases not exposed*controls exposed)

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in case-control study you should use ___ to measure cases

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incidence

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little improvement in precision is achieved once control/case ratio is above ___

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4

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4 disadvantages of case-control study

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prone to recall bias
prone to selection bias in controls
only an approximation of risk
not suitable for rare exposures

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in cross-sectional study risk is measured by ___ (2)

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prevalence odds ratio
prevalence ratio

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4 disadvantages of cross-sectional study

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no temporal relationship
biased towards long-duration cases
no risk ratio
not suitable for rare diseases or exposures

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T/F: systematic error does not decrease with increased sample size

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true

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3 sources of systematic error

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selection bias
information bias
confounding

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3 a priori criteria for confounders

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risk factor for disease
associated with exposure in source population
NOT an intervening variable in the causal pathway

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3 ways to control confounding in experiment design

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restriction of study
randomization
matching

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3 ways to control confounding in data analysis

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restriction of analysis
stratification
multivariable regression

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validity is aka

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accuracy

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reliability is aka ___ (2)

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repeatability
precision

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___ is a function of systematic errors

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validity

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___ is a function of random errors

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reliability

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___ errors are reduced with increasing n

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random

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T/F: bias only affects external validity

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false

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1st 5 of Hill's criteria for causality

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strength of association
consistency of association
specificity: single effect of exposure
temporality
biological gradient (dose-response)

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last 4 of Hill's criteria for causality

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biological plausibility
coherence with literature
experiment
analogy

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___ determines the gain from performing a test

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difference between pre-test and post-test probabilities

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pre-test probability is estimated by ___

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prevalence

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post-test probability is estimated by ___ if test is positive, ___ if test is negative

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PPV
1-NPV

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solution to lead-time bias in evaluating screening programs is ___
solution to length-time time bias in evaluating screening programs is ___

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use mortality instead of survival time
use RCT

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screening test should have high ___

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sensitivity
specificity
PPV

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recall bias is an example of ___ bias

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measurement/infomation