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54 Cards in this Set

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rate
number of cases/population/per unit time
measures of moribity:
a.incidence rate
b.attack rate
c.secondary rate
d.prevelance
e.incidence
d.point prevlance
e.peroid prevelance
Incidence rate
# of new cases/population (per time)
*10^5
Attack rate
# of new cases during epidemic/population at the start of the epidemic
*10^2
Secondary attack rate
# of new cases among contacts of known cases/size of at risk population
*10^2
*# ill/#contacts
Prevlance
most effective in chronic illnes
Incidence
short duration
point prevalance
# current cases/estimated population
*10^5
peroid prevelance
# current cases in time interval/est pop
*10^5
Confidence Interval
%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
Risk ratio
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
Odds ratio
estimates the RR-is good when disease is rate
*(a*d)/(b*c)
Measures of morality
a. crude death rat
b. specific death rate
c. proptionate moraltiy
d. case fatality rate
a. crude death rate
#deaths/population
10^3 or 5
b. cause-specific death rate
# deaths d/t cause//population
*10^3
c. porportionate moratlity
#deaths d/t cause//total deaths
*10^2
d. case fatality rate
# fatalities d/t case/# cases
Case definition
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
what's included in descriptive epidemiolgy
who
what
where
when
What's included anaytical studies
1. experimental study includes the study design*** (see more notecards)
Study design: includes lots of things--anme the first 2
1. who are the subjects-establish entry criteria
2. need for a comparision gorup-new drug vs. old drug or placelbo
What are the next three things a study design involves:
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
What the 6th part of the study disgn?
Intention to treat..
a. same outcome as income
b. favors null hypthesis where there's no relationship bw exposure and outcome
The 7th part of study design is outcome and includes what 4 things?
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
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!!
Analytical
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
What are the three types of observational studies:
a. cohort
b. case-controlled study
c. cross sectional study
Desribe cohort study
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
Describe case-control study
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
Describe cross-sectional study
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
What is the other type of analytical epide study that's not observational?
experimental-where epi/scientist controls the exposure in the pop
Reiteration: RR
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
What does it mean if RR=3 with 95% (.2-.8)
There's a reduction in disease in 70% of ppl who were exposed; exposure was protective
*strong associ
confidence intervals
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)
What is casuation?
an approach to scientific inference that's easier to test in a population versus an inviduval
Causation: inductivisim
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
Casuation: refutationism
kill the rooster and the sun comes up--i hae refuted the hypthesis
Causation: consensus:
scienfitic community determines validity of theories
Causation: how does science advance?
by process of conjecture and refutation--therize then disprove
Hill Casual Criteria
developed by Bardford Hill: all scienfic work is incomplete
strength of association
a.strong assoc are more likey to be causal
b. weak assoc are more liley to be d/t bias
Consisntency
lack of consistency doesn't rule out causation
specificty
single cause leads to single effect
specificity
single cause leads to a single effect
ex.vinyl chorlide-leads to liver cancer
temporality
cause precedes effect
biologic gradient
more experiments-more disease
1. monotonic dose-response curve
plausability
is there a logical biological explanation
coherence
cause and effect hypthesis gives a choherent explanation for evidence
experimental evidence
hypothesis is consistent w/results
analogy
the similarity bw this hypthesis and accpeted hypthesis
Surveillance:
ongoing collection of health data: involves three types
1. passive
2.active
3. enhanced
passive ****
most used; health dept waits for cases to be rpsoted by docs/hospitals
active
health dept contacts docs by person/phone
enhanced passive
health dept mails/faxes sheets to docs requesting data