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31 Cards in this Set
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Epidemiology Defn
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the study of distribution and determinants of health states/events in specified populations and the application of this study to control health problems.
We describe by frequency and pattern (t, place, characteristics). We test preventive and therapeutic interventions thru ideal/research conditions to measure efficacy or through routine elivery to measure effectiveness. |
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2 types of epidemiology study
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1) descriptive: distribution outcomes by age/type/geography/over time
Exp: descriptive studies, census, health survey,routine monitor, birth/death record, reporting of diseases 2. Analytical: a. Observation: ecological, cross-sectional, cohort, case-control studies. b. Intervention: RCT's, nonrandomized studies Tries to find factors that inc/dec probability/risk of outcome |
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Sufficient Cause
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factor(s) that inevitably produces the outcome
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Necessary causes
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single necessary cause is rarely sufficient to cause an outcome
make up sufficient causes |
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Causality
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relating a causative agent or risk factor (aka exposure) to an outcome of interest. The exposure always preceeds the outcome.
Support for causality: dose-response, strength of association, plausible biological mech of action, reproducibility of result. Analytical methods can confirm association b/t exposure and outcome but causality can only infer if alternative explanations have been accounted for by chance/bias/confounding factors |
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Chance
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=possibility of random error
Decrease by inc pop size, use random selection (observational studies) or randomization (intervention studies) |
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Bias
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systematic differences between comparison groups which may misrepresent the association being investigated
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Confounding
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another factor independently assoc w/ both outcome and exposure, that influences the association being investigated.
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Hypothesis
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proposed association
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Observational study
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compares frequency of outcome in groups/individuals with and without exposure of interest
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Intervention Study
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Experiment to evaluate the effect of decreasing a risk factor or increasing a protective factor on the frequency of an outcome.
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Ecological study
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Goal is to relate total frequency of an outcome to the average level of exposure in a population.
Exp.: EtOH use and inc breast cancer incidence |
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Cross-sectional study
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Collect data on outcome and exposure at 1 point in time from random sample of study subjects.
Exp. prevalence of HIV and male circumcision |
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Cohort
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compare individuals with recorded difference in exposure to measure occurrence over time of the outcome in relation to the exposure.
Exp. Incident of cervical cancer in women with and without HPV |
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Case-control
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Identify individuals with and without outcome and examine whether they differ in relation to prior exposure.
Exp. cell phone use with brain tumor compared to those without tumors. |
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Intervention
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Allocate a protective factor to individuals/groups and compare frequency of outcome in those exposed to those unexposed. Can be randomized/nonrandomized.
Exp. Incidence of malaria in kids with insecticide net to those with untreated net. |
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Calculate risk per
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10,000
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Case definition
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Criteria for identifying an individual as having the health outcome of interest, which may specify clinical signs and symptoms, diagnostic test results, and time period.
Exp: malaria case= fever in 48h and +blood smear |
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Ways to measure frequency
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PRIO
Prevalence Risk Incidence Rate Risk, Odds, and Incidence Rate are ways to consider Incidence Odds |
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Prevalence
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# existing cases in defined population at defined point in time divided by total population at that time.
# cases/total population (at specific time) |
Can't be >1, usually present as percent without units
AKA point prevalence (NOT period prevalence) |
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Period Prevalence
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# cases of outcome over specific timeframe / population at that short time period
Is a proportion |
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Incidence
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Frequency of new cases in defined population during a specific time.
Measure with ecological/cohort studies. Measure with ecological (observational of a population) and cohort (f/u study where 2 groups are defined on basis of exposure to potential risk factor and f/u over time to measure incidence of outcome, which is then compared b/t groups to give an estimate of relative risk. |
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3 ways to consider incidence
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risk, odds, incidence rate
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Risk
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= cumulative incidence
Proportion that is never >1 and can put as % over amount of time. Risk=#new cases / total # individuals at risk in population at spec time |
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Secondary Attack Rate
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Used in investigating outbreaks
# of new cases among contacts / total # of contacts at spec time |
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Odds
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# new cases/# noncases at spec time
Exp if 75 out of 100 catch a cold then odds is 3:1 of catching a cold. |
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Incidence Rate
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accounts for variatin in time at risk and need units
# new cases/total person-time at risk during specific time |
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Person-Time at Risk
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Sum of time each individual in a defined population is at risk of an outcome.
Is denominator in incident rates. Frequently use 1000 person-yrs at risk but can use person-days, person-months In registry data/large studies, it may be difficult to know perseon-time exactly for each individual in the population and then we use the population at mid-point of the time-period of interest multiplied by period of time under consideration to given an estimate of person-time at risk so long as population doesn't change substantially over the study period. |
Exp. 750 cases of breast cancer occurred b/t 2005-2010 with a population of 10,130 in the year 2007-2008
Incident rate= 750/ (10,130 x5)= 0.015 per person-year at risk or 14.8 cases per 1000 person years at risk between 2005-2010. |
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Study population
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=cases + noncases
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Case definition
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defined poopulation considered a + case
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Secondary contacts in setting of vaccine
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# cases in secondary contacts/#unvaccinated or unprotected contacts
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