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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 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