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| Pregunta | Respuesta |
| 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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