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71 Cards in this Set

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Prevalence
ex: % of people in dominica with diabetes today
proportion of persons in a defined population that has the outcome of interest at a defined point in time (both old + new cases)
Incidence
what are 3 measures used?
measures frequency of new cases
(risk, odds, rate)
Risk
probability of outcome occurrence in an outcome free population during a specified time period
Odds
ratio of probability of getting the disease to the probability of not getting the disease during a given time period
Rate
aka
incidence rate or
incidence density
expresses the # of people or events in relation to the total population at risk
(includes time frame)
"person time at risk"
age specific rates
vs
crude rates
-used for a specific age group
-rates that aren't age specific
case fatality rate
proportion of cases of a specified cause which die in a specified period of time
cause specific mortality rate
# of deaths by a specific cause in a defined population in a defined period of time
infant mortality rate (IMR)
# of deaths in children under 1 year of age divided by the # of live births in same time period in a specified population
maternal mortality rate
# of maternal deaths divided by the # of woman in the reproductive age (15-49) in a given yr
perinatal mortality rate
# of fetal deaths (22wks gestation or more) and early neonatal deaths (0-7days) in a year, in a defined population, divided by the total # of live births and fetal deaths in the same population and time period
Survival rate
proportion of survivors in a group usually patients with a dz who survived in a specified period of time
Rate ratio
measure of the strength of the association b/w a risk factor and a dz
**exposed/unexposed
vehicle
mode of transport of an infectious agent through the environment to a susceptible host
vector
a living carrier= usually an arthropod; that serves as a mode of transport for an infectious agent from an infected host to a susceptible host
reservoir
the primary habitat in which an infectious agent survives and reproduces
carrier
a person/animal that harbors a specific infectious agent in the absence of discernible clinical disease and serves as a potent source of infection
asymptomatic carrier
subclinical throughout the infectious carrier state
incubationary carrier
infectious carrier state occurs during the incubation period preceding clinically recognizable disease
convalescent carrier
infectious carrier state continues during convalescence when clinically recognizable disease is no longer present
exposure period
time during which an individual or group is exposed to source of infection
incubation period
time from initial infection (entry of infection) to onset of clinical illness. (usually expressed as the median or arithmetic/geometric mean, min, and max of incubation period)
Infectious (or communicable) period
period during which an infected person is able to transmit the infectious agent. (important to know this for various agents in order to impose appropriate control measures)
latent period
time from receiving infection to onset of infectiousness. (minimum interval between successive infections in a chain of transmission)
serial interval or generation time
interval b/w the same stage of illness in successive cases in a chain of transmission. (only applicable when infection spreads form person to person)
Common source outbreak
(point vs extended)
transmission of an infectious agent involving a source that is common to all outbreak-assoc cases
-brief common exposure (1 incubation period)
-present over days/wks (may be continuos of intermittent)
propagated/progressive outbreak
series of progressively taller peaks one incubation period apart (not many outbreaks have this classic pattern)
what is the preferred measure of association for cross sectional studies?
chi-square test
Cohort studies
starting point is definition of a group of people by their exposure status
Case control studies
(retrospective study)
starting point is the definition of a group of people with a particular dz or condition (outcome)
**ALWAYS analytical
Confounders
"alternative explanation"
-other risk factors that may contribute to an apparent association b/w the exposure of interest and the outcome (may be unknown)
Intervention study #1
= field trial
trials to prevent disease (difficult to carry out)
Intervention study #2
= clinical trial
trials to evaluate one or more new tx's for a disease or condition
Drug trial classification
Phase I
first drug experiments with human trials, determines single acceptable dose, metabolism, bioavailability, dosage, 20-80pts
Drug trial classification
Phase II
initial clinical investigation for tx effect: small scale into effectiveness and drug safety, screening process, about 100-200 pts
Drug trial classification
Phase III
Full scale evaluation of tx: after drug is shown to be effective its compared w/ current standard tx
(MOST rigorous and extensive clinical investigation of new tx)
Drug trial classification
Phase IV
Post marketing surveillance: monitoring for adverse effects and long term studies of morbidity and mortality
Target population
general group to whom the investigators expect the results of the trial to be applicable
Experimental population
subset of the target population selected for the purpose of conducting the survey
Study population
those who are eligible and willing to enroll in the trial
Randomization (allocation to study groups)
a method which allows chance and only chance to determine the assignment of subjects to various groups (eliminates bias and creates comparable groups)
Factorial design
technique used to test two or more hypotheses simultaneously
Crossover trials
each subject acts as his/her own control by receiving at least 2 different interventions at different times after a 'wash-out' period
Blinding/masking
patient is unaware as to whether he/she is receiving the intervention under study
Double blind study
(the more subjective the outcome the greater rationale to use this!!! ex: pain)
when BOTH patient and investigator DO NOT know whether the subject is receiving intervention of control
Survival analysis
examines patient survival following diagnosis or following surgical therapeutic procedure or treatment (or from birth, or a major historical event)
Casual association
a change in frequency or quality of an exposure results in a corresponding change in the frequency of the disease or outcome of interest
Random error (chance)
random variation from sample to sample can account for observed association
**Sample size matters!
P-Value
-used in what?
a measure that often reported from all tests of statistical significance (quantifying the degree of chance variability)
P-Value definition
the probability of observing that an effect at least extreme as that observed in a particular study could have occurred by chance alone
Confidence interval
gives information (on p-value in terms of deciding whether an assoc is statistically significant or not) "level of variability"
Bias
said to exist when some aspect of the design or conduct of the study has resulted in an alternative explanation for the observed results
-deviation from the truth
Selection bias
when there's a difference b/w the characteristics of the people selected for the study and the characteristics of those who weren't
Information bias
<errors can be introduced by the observer, responder, or instruments used>
occurs when measurements or classification of disease or exposure are not valid (not measuring what it's supposed to)
Confounding
occurs when the effects of two associated exposures/risk factors have not been separated and its incorrectly concluded that the effect is due to one rather than the other
Interaction/effect modification
occurs when the presence of one factor modifies the effect of another
Casuality=

what criteria is used?
if chance, bias, and confounding don't seem to explain an observed observation, consider a casual assoc.
-Bradford Hill criteria
What is the #1 essential of the Bradford criteria?
The exposure must precede the outcome if the relationship is casual
Meta-analysis
a technique used to combine results from various studies
Screening
presumptive identification of unrecognized dz or defect by the application of tests, examinations, or other procedures which can be applied rapidly (sorts out well people) NOT Diagnostic!!
Primary prevention
targets asymptomatic people to ID early risk factors for the dz so pathologic process can be interrupted BEFORE symptoms develop
Secondary prevention
targets persons who are early in the dz process so as to improve prognosis
"PAP smear"= papanicolaou smear>detects HPV before pts develop cervical cancer
Tertiary prevention
targets persons who are developing complications in order to reduce the impact of the sequelae of such complications
Screening test validity
extent to which test actually measures what its supposed to measure
Sensitivity
ability of the screening test to identify those who are developing the disease
TP/TP+FN
Specificity
ability of the test to give a negative result when those tested are not developing the disease of interest
TN/TN+FP
Positive predictive value
likelihood that someone with a positive test result has the disease
TP/TP+FP
Negative predictive value
likelihood that someone with a negative test result doesn't have the disease
Reliability
degree to which the results obtained by a measurement procedure can be replicated
Standardization/adjustment
procedure through which a summary rate is produced which takes into account the differences in population structure
Vital statistics
systematically tabulated information concerning births, marriages, divorces, separations, and deaths based on registration of these vital events
"statistics of health, sickness, disease, and death