POPH192 L17-19 Flashcards
Epidemiology
The study of distribution (descriptive) & determinants (analytic) of health related States or events in specified populations
Descriptive Epidemiology
Person, place, time
(what is it; who is involved; where; when it occurred)
- observational
Analytic Epidemiology
Quantifies association btwn exposures & outcomes (why we see relo btwn exposure & outcome)
- causation
- observation/intervention studies
Cross-sectional Studies
Measures exposures &/or outcomes at one time pt.
What is CSS used for
- describe prevalence of exposures/health conditions in pop
- compare prevalence
- generate hypotheses
- plan (e.g., health service delivery)
What does CSS measure?
Prevalence: proportion of defined pop who have disease at a pt in time
CSS Strengths
- can assess multiple exposures & outcomes at same time
- depending on research q (might be suitable); can measure prevalence, distribution of prevalence in pop, hypothesis generation
- less expensive/relatively quick
CSS Limitations
- can’t establish temporal sqnce (exposure or outcome first?
- doesn’t measure incidence (onset of disease)
- not good for studying rare exposures/outcomes
- not good for studying transient/variable exposures/outcomes
Ecological Studies
Compare exposure & outcomes across GROUPS not individuals (like countries)
What is EcS used for?
- compare btwn pop
- assess pop lvl factors
- consider hypotheses
EcS Strengths
- depends on research q
- pop lvl exposures
- consideration of hypotheses - data often routinely colleted
- relatively easy to do/inexpensive
EcS Limitations
- ecological fallacy (when association found to occur at group lvl doesn’t occur at individual lvl)
- can’t control confounding
- can’t show causation
Comparison Group Importance
- est how common outcome is in ppl w/ out exposure we’re looking at
- determines whether exposure is associated w/ outcome (if occurrence of outcome is diff btwn the two groups, suggests exposure is associated w/ change in risk of outcome)
Outcome more common in exposed group
Exposure is a risk factor for outcome
Outcome less common in exposed group
Exposure may be protective
PECOT
Population - group of ppl in study
Exposure - what potential determinant is
Comparison - what potential determinant is being compared to
Outcome - health outcome being assessed
Time - how long ppl are followed up
Measures of Association
Relative Risk (ratio) & Risk Difference
- quantify degree to which an exposure increases/decreases occurrence of outcome
Relative risk (ratio)
How many times as likely exposed group will develop outcome that comparison group
- Exposed/Comparison = Relative Risk
Risk Difference
How many extra/fewer cases of outcome in exposed group are attributable to exposure?
- reported differently for incidence proportion & incidence rate
Greater Incidence of outcome in Exposed group
Bad outcome, exposure is potentially risk factor for outcome
Same Incidence of Outcome
Exposure doesn’t change occurrence of outcome THUS no association btwn exposure & outcome
- this is Null Value
Greater incidence of outcome in comparison group
Bad outcome, exposure is potentially protective factor for outcome
Interpreting RR
Exposed Group, Owners of dogs w/ T2D
Outcome, were 1.38x as likely
Value, to develop T2D
Comparison Group, as owners of dogs w/ out T2D
Risk Difference
How many fewer/extra cases of outcome in exposed group are attributable to exposure
- Null value = 0
Cohort Study
Analytic-Observational: observing ppls exposures & what happens to them
- individuals defined on basis of presence/absence of exposure to suspected risk factor
Cohort Studies Strengths (4)
- determines temporal sequence btwn exposure & outcome
- examines multiple outcomes from exposure
- can calculate incidence (& thus RR & RD)
- good for studying rare exposures
Cohort Studies Limitations (6)
- Loss to follow-up may lead to bias
- potential for misclassification of exposures/outcomes
- generally not good for studying rare outcomes
- time consuming + expensive
- can be inefficient w/ transient/acute exposures
Prospective Cohort Study
Starts at exposure
Historical Cohort Study Strengths
Starts at Outcome
- less time consuming + inexpensive
- good for outcomes that take long time to develop
HCS Limitations (3)
- Quality of data unknown
- all relevant factors not considered
- selection bias (selection of data)
