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35 Cards in this Set
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Epidemic spread 
common source: group of persons are all exposed to an infectious agent or toxin from same source point source: type of common source where individuals become ill within one incubation period propagative: occurs from transmission from person to person over more than 1 incubation period 

Adjusted estimation 
reported cases serve as lower bound calculations based on a model determine upper bound midpoint is best guess to how many cases were actually seen 

Types of prevention 
primary prevention: prevents onset of risk behaviors > decreases incidence (eg health education that promote healthy living) secondary prevention: screens for risk factors and early detection of asympt or mild dz > decreases prevalence (eg community BP screening, MD support to quit smoking) tertiary prevention: reduces longterm impairment or disabilities > decreases recurrences and slows dz progression (graded aerobic activity during recovery from MI) 

Adjusted rates 
calculated after using statistical procedures to minimize demographic differences btwn populations being compared 

Prevalence rate 
proportion of individuals with existing dz at a point of time prevalence = (ppl with existing dz / population of ppl at risk for dz) x multiplier point prevalence > prevalence at a given time period prevalence > prevalence over period of time good for chronic dz 

Incidence rate 
proportion of individuals developing new dz during a period of time can only be calculated over a period of time incidence rate = (ppl with dz onset / population at risk for dz) x multiplier good for acute conditions 

Prevalence pot 
determined by rates of incidence, recovery, and death prevalence = incidence x duration 

Number needed to treat 
how many ppl do you need to treat to prevent 1 case inverse of incidence rate if incidence 16 per 1,000 (16/1000) then NNT = 1000/16 = 62.5 if comparing two modulaties it is the inverse of absolute risk reduction (ARR) > 1 / (incidence A  incidence B) where ARR = incidence A  incidence B 

Number needed to harm 
1 / (incidence of exposed  incidence of nonexposed) 

Infant mortality 
# deaths within 1yr of age / total births AA have highest rates of infant mortality bc of low birth weight & infections Native Americans have highest rate of SIDS 

Infant mortality risk factors 
maternal age (younger worse) poverty single parent family 

Years of potential life lost 
sum of yrs that ppl would have lived had they experienced normal life expectancy if life expectancy is 75 & person dies at 65 then YPLL is 10 

Positive predictive value 
true positive / (true positive + false positive) if test is positive what is the probability that someone has the dz this is dependent on specificity 

Negative predictive value 
true negative / (true negative + false negative) if test is negative, what is probability that someone doesnt have dz this is dependent on sensitivity 

Types of studies 


Observational vs experimental studies 
observational: no intervention, just observe natural course experimental: there is an intervention and study determines the effect of the intervention 

Different types of observational studies 
1) case report: single clinical subject or event with no control 2) case series: characterization of a group of clinical subjects 3) crosssectional study: presence or absence of dz determined in each member of the study population or in a representative sample at a particular time > interested in prevalence but cause and effect cannot be determined (study is at a given time) data analyzed with chisquard test 4) casecontrol study: identifies a group of ppl with a dz and group w/o dz then compares them for risk factors > mostly retrospective (study is of the past) data analyzed with odds ratio 5) cohort study: identify population who has been exposed to risk factor & is followed over time and compared with a group not exposed to the risk factor > prospective (study is following through the future) data analyzed with relative risk 

Relative risk 
goal of observational study incidence rate of exposed group / incidence rate of unexposed group 

Attributable risk 
how many more cases in one group? incidence rate of exposed group  incidence rate of unexposed group 

Odds ratio 
odds of exposure for cases / odds of exposure for controls used for casecontrol studies 

3 phases of clincial trial 
Phase I: safety in healthy volunteers
Phase II: protocols and drug levels in small groups of patient volunteers (couple of 100) Phase III: efficacy and occurrence of side effects in larger group of patient volunteers 

Different types of randomized controlled clinical trials 
1) double blind: neither subjects nor researchers know whether the subjects are in the tx or control group 2) community trial: therapeutic regimen received by an entire community 3) crossover study: for ethical reasons, no group involved can remain untreated; all subjects receive intervention at different times 

Types of bias 
selection bias: sample is not representative of population (Berkson's bias) measurement bias: information is gathered in a manner that distorts the information (Hawthorne effect > subject knows they are being evaluated so that changes performance) experimenter expectancy: experimenter's expectations inadvertently communicated to subjects (Pygmalion effect) lead time bias: gives a false estimate of survival rates recall bias: subjects fail to accurately recall events in the past latelook bias: individuals with severe dz are less likely to be uncovered in a survey bc they die first confounding bias: the factor being examined is related to other factors of less interest 

Variance and STD 
variance = (value  mean)^2 STD = sqrt (variance1 + ... + varianceN / N) +/1 STD cover 68% of values are within mean +/ 2 STD cover 96% of values are within mean 

Standard error 
SE = STD / sqrt (N) 

Skewed curves 
negatively skewed > mean < median < mode (tail skewed to left) positively skewed > mean > median > mode (tail skewed to right) 

Confidence interval and significance 
if 95% CI overlap then not significant
if there is no overlap, then significant 

Relative risk and confidence interval 
if 95% CI does not contain 1.0 then is significant if RR is >1 and CI does not contain 1.0 then there is a significant increased risk if RR is <1 and CI does not contain 1.0 then there is a significant decreased risk 

Type I (alpha) error 
rejecting null hypothesis when it is really true > think something is significant when it's not if pvalue = 0.05 > type I error is 5 in 100 (aka 1 in 20) 

Type II (beta) error 
fail to reject null hypothesis when it is false > think something isnt significant when it is type II error= 1power 

Power of study 
capacity to detect a difference if there is one 

Chisquare test 
you know what to expect and testing whether you are seeing that or not eg toss coin 10x, you expect 5 heads & 5 tails 

ttest 
independent group: test 2 independent groups paired sample: each group is measured 2x, once before and once after intervention one group: have only 1 group but want to compare to imaginary group 

Length time vs lead time bias 
both involve screening tests length time  testing for a dz that can have rapid or indolent progression & screening just selects for those with an indolent course thereby leading to impression screening improves survival lead time  advent of new screening test picks up test earlier but there is no change to actual duration to mortality (increasing sensitivity picks up dz earlier) 

Likelihood ratio 
Positive LR = sens / (1spec) Negative LR = (1sens) / spec prob of given test result occurring in a pt with a disorder compared to the prob of the same result occurring in a pt w/o the disorder not dependent on disease prevalence as PPV and NPV are 