# EPM101 (Fundamentals of Epidemiology)

Flashcards by jmoffman, updated more than 1 year ago Created by jmoffman over 6 years ago 39 1

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Flashcards on EPM101 (Fundamentals of Epidemiology), created by jmoffman on 06/01/2014.

## Resource summary

 Question Answer Attributable risk (AR) No of cases attributable to exposure in exposed group AR = risk (exposed) re - risk unexposed) ru Population attributable risk - Compares risk of an outcome in the population as a whole with risk in unexposed individuals only - Estimates impact on population by removing or changing distribution of exposure risk in exposed group RR x ru Attributable fraction (AFe) attributable risk as a proportion of the total risk in they exposed group AFe = (re - ru) / re or AFe = (RR-1) / RR Afe is a relative effect <=> excess risk relative to total risk Preventable fraction (PF) Use if exposure has preventable effect PF = (ru - re)/ru or PF = 1-RR Population attributable risk (PAR) - excess risk in total population due to exposure - compares risk in total population to that in unexposed group Population attributable fraction - percentage of total risk attributable to exposure - dependent on prevalence of exposure - dependent on population being studied Basic reproductive no R0 - average no of infected 2ary cases produced by each infected case in a totally susceptible population - R0 = c x p x d c = no of contacts made per unit of time p = probability of transmission per contact event d = duration of infectiousness of the case Net reproductive rate average no of vary infectious cases per case in a population where not all individuals are susceptible R = R0 x x= proportion of susceptible population x=a/L L= average life expectancy a=average age of infection Herd immunity resistance of a group to an attack by a disease to which a large proportion of the members of the group are immune HI = 1-x Conditions for herd immunity - disease restricted to single host species and transmission direct from one to another - no other means of transmission - infection must induce immunity Herd immunity threshold (HIT) - Percentage of population required to be immune for the disease to become stable HIT = 1 - (1/R0) = (R0 -1)/R0 Standardisation Control for confounding by age by stratification Direct standardisation Take observed age-specific mortality rates from each population a apply to a specified standard population with know age structure => age adjusted number of deaths for each study population To calculate standardised mortality rates - step 1 multiply each age specific mortality rate by no of people in the corresponding age category in the standard population To calculate standardised mortality rates - step 2 Take expected no of deaths if standard population age structure and divide by total no of person-years in standard population Comparative mortality figure - age standardised rate ratio - divide age-adjusted rate for one country / region by that for another country - independent of differences in age structure between the populations Indirect standardisation Calculate no of deaths expected if both populations had same (standard) age-specific death rates, but kept real age structure For indirect mortality need to know - Age specific mortality rates for standard population - Age structure of study population - Total no of deaths in study population Calculate indirect mortality rate by applying set of standard age-specific death rates to the real age structure of study population and compare total no of expected with observed Standardised mortality ratio (SMR) rate of observed over expected Observed deaths / expected deaths usually multiplied by 100 and expressed as percentage Validity how close the test comes to measuring the variable we are interested in Reliability How consistent the test is when used by a different observer Sensitivity proportion of true positives correctly identified by new test a/(a+c) Specificity proportion of true negatives correctly identified d/(b+d) Positive predictive value proportion of individuals with positive result who have the disease a/(a+b) Negative predictive value proportion of individuals with neg result in the new test who do not have the disease d/(c+d) Proportional mortality ratio (PMR) (proportion of deaths from specified cause (exposed) / proportion of deaths from specified cause (comparison population) ) x 100%= mean pair agreement index (a+d)/(a+b+c+d) Kappa value of less than 0.5 regarded poor agreement and >0.75 indicates excellent agreement

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