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54 Cards in this Set
- Front
- Back
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rate
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number of cases/population/per unit time
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measures of moribity:
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a.incidence rate
b.attack rate c.secondary rate d.prevelance e.incidence d.point prevlance e.peroid prevelance |
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Incidence rate
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# of new cases/population (per time)
*10^5 |
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Attack rate
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# of new cases during epidemic/population at the start of the epidemic
*10^2 |
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Secondary attack rate
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# of new cases among contacts of known cases/size of at risk population
*10^2 *# ill/#contacts |
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Prevlance
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most effective in chronic illnes
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Incidence
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short duration
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point prevalance
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# current cases/estimated population
*10^5 |
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peroid prevelance
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# current cases in time interval/est pop
*10^5 |
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Confidence Interval
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%95 measns that you are 95% condifent all of the time
*so 95% of the time, you'll fall in the range *5% of the time, you'll be o/side the range |
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Risk ratio
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risk for group of interest: risk for comparison group:
1. coleslw ex-at coleslw 9 sick, 1=not sick attack rate9/10=90% 2. didn't eat coleslwa 1=sick 9=not sick attack rate=1/10=10% *so risk ratio is .9/.1=9 so ppl who ate the coleslwa re 9x as liely to get sick as the group that didn't eat the slaw |
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Odds ratio
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estimates the RR-is good when disease is rate
*(a*d)/(b*c) |
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Measures of morality
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a. crude death rat
b. specific death rate c. proptionate moraltiy d. case fatality rate |
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a. crude death rate
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#deaths/population
10^3 or 5 |
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b. cause-specific death rate
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# deaths d/t cause//population
*10^3 |
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c. porportionate moratlity
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#deaths d/t cause//total deaths
*10^2 |
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d. case fatality rate
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# fatalities d/t case/# cases
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Case definition
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used yb epidemologist s to define who has the disease*always look for this in case deinition in study
1. used for surveillance 2. used for studies-either observational or experimental 3. decides who they're going to include |
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what's included in descriptive epidemiolgy
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who
what where when |
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What's included anaytical studies
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1. experimental study includes the study design*** (see more notecards)
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Study design: includes lots of things--anme the first 2
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1. who are the subjects-establish entry criteria
2. need for a comparision gorup-new drug vs. old drug or placelbo |
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What are the next three things a study design involves:
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3. random assignment of treatment (not always possible)--observational comparison are rarely definitive
2. compulsive c+-treat grps identical 3. crossover deigsn-subj serves as their own contorl*bad if they drop out |
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What the 6th part of the study disgn?
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Intention to treat..
a. same outcome as income b. favors null hypthesis where there's no relationship bw exposure and outcome |
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The 7th part of study design is outcome and includes what 4 things?
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1. it must be measurable-death, lab results
2. must be clincaly relevant to health 3. How sure are we that there is a diff bw pops? 4. P<0.05-less than 5% chance that the difference is due to coincidence--statisically different |
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Describe descriptive vs. analytical epidemology
well describe descriptive first |
descriptive-asks: who, waht when, where, when, where
1. there's no comparison group 2. measures morbidity and morality 3.use descriptive epidemology to suggest hypothesis, NOT TO TEST THEM!! |
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Analytical
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Asks: how, why
1. there is a comparison group 2. measures association..OR, RR 3. 2 types: observational(where OBSERVES and measures risk factor in population)and experimental |
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What are the three types of observational studies:
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a. cohort
b. case-controlled study c. cross sectional study |
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Desribe cohort study
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start w/dz free pop; good w/common dz
1. follow a pop over time and look at risk factors ass w/devleopment of dz 2. has limiations: need larg N, expensive, time consuming; lose subjects d/t floow up 3. advangtes: it decreases bias |
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Describe case-control study
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start w/dz pop; good w/rare dz; look at risk factors in diseased vs. non-diseased populations
1. limitations-accuracy, did dz cause rf or vice versa? 2. advantages-quick,cheap, more efficient for rare dz-use OR to estimate RR |
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Describe cross-sectional study
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not used often, good if money is low;
1. describes pop at time of study 2. exposure and dz are look at toghether 3. limiations 4. CANT MAKE CAUSAL INFERENCE-this is bc you don't know which came first-the risk factor or dz-- 5. advangtes are cheap and quick |
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What is the other type of analytical epide study that's not observational?
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experimental-where epi/scientist controls the exposure in the pop
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Reiteration: RR
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How big is the difference b/n the 2 groups?
RR=16 95% CI (8-667); then DZ is 16x more likey in exposed vs. unexposed *strong ass bc there's an increase RR and CI is far from 1 |
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What does it mean if RR=3 with 95% (.2-.8)
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There's a reduction in disease in 70% of ppl who were exposed; exposure was protective
*strong associ |
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confidence intervals
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how big is the zone of uncertainity around the RR
1. CI gives margin of error-gives the interval that your results will fall 95% of the time 2. if CI includes 1-there is no association (.7-1.9) |
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What is casuation?
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an approach to scientific inference that's easier to test in a population versus an inviduval
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Causation: inductivisim
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we make the same observation repeatedly then we make generalizations from it-
1. obseravation leads to generalization 2. rooster causes the sun to come up |
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Casuation: refutationism
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kill the rooster and the sun comes up--i hae refuted the hypthesis
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Causation: consensus:
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scienfitic community determines validity of theories
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Causation: how does science advance?
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by process of conjecture and refutation--therize then disprove
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Hill Casual Criteria
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developed by Bardford Hill: all scienfic work is incomplete
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strength of association
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a.strong assoc are more likey to be causal
b. weak assoc are more liley to be d/t bias |
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Consisntency
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lack of consistency doesn't rule out causation
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specificty
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single cause leads to single effect
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specificity
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single cause leads to a single effect
ex.vinyl chorlide-leads to liver cancer |
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temporality
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cause precedes effect
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biologic gradient
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more experiments-more disease
1. monotonic dose-response curve |
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plausability
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is there a logical biological explanation
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coherence
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cause and effect hypthesis gives a choherent explanation for evidence
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experimental evidence
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hypothesis is consistent w/results
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analogy
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the similarity bw this hypthesis and accpeted hypthesis
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Surveillance:
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ongoing collection of health data: involves three types
1. passive 2.active 3. enhanced |
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passive ****
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most used; health dept waits for cases to be rpsoted by docs/hospitals
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active
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health dept contacts docs by person/phone
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enhanced passive
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health dept mails/faxes sheets to docs requesting data
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