EPI Final Exam Flashcards
How to Calculate Prevalence Period
existing cases at start + new cases over a period of time/ size of population at start of time period = %
How to calculate prevalence point
existing cases at “point” in time/ size of population at “point” in time = %
a single point in time
how to calculate incidence proportion (cumulative incidence= CI)
number of people developing the outcome/ number of people at risk
CI=IR x time
estimation for risk in a population “at risk” (candidate population)- fixed population
how to calculate incidence rate (IR)
number of people developing the outcome/ total time at risk
estimates change in risk over time in a population at risk- fixed or dynamic population (instantaneous risk)
how to calculate incidence density
number of new cases / sum of the person-time of the at-risk population
how to calculate person time incidence
the number of new cases/ person time at risk through observation
how to calculate crude death rate
number of death in a given period/ the population exposed to risk of death in that period
how to calculate proportionate mortality
number of deaths from a given cause in a specific period of time/ total number of deaths in the same period
how to calculate case fatality rate
proportion of individuals with a disease who die from the disease
what is age adjustment
standardization
- provides a valid comparison using a single number for each population
- transform a measure based on a specific factor composition of a reference population
- referred to as the direct method of standardization
why is age adjustment used
almost all diseases occur at different rates in different age groups, so for accurate analysis- its going to be important to take this into account
what are age specific rates
total number of health events for the specific age group of interest/ total population in that age group
how are age specific rates used
multiplying the age-specific rates of disease by age- specific weights
what is the formula for risk difference/excess risk
Re-Ru/Ru = RR -1 (expressed as percent
the null value is 0%
not a proportion just a ratio
“relative risk”- often described as the percent change relative to the reference risk
what is the formula for risk ratio
RR = Re/ Ru
Risk ratio & rate Ratio
Rate Ratio : Rr = IRe/ IRu
Prevalence ration = Pe/Pu
what is the formula for odds ratio
(a/b)/ (c/d) or ad/bc
what is the formula for relative risk
deaths or disease risk in a specific population/ risk of people from all other groups
how do you calculate and interpret risk difference/excess risk
RE-Ru/Ru = RR -1 (expressed as a percent)
- increase linearly above one and exponentially below one
RR= Rm/Rf and RR = Rf/Rm
how do you calculate and interpret risk ratio
no effect (null value) is 1.0 RR >1 indicates GREATER risk for exposed population relative to reference population
RR < 1 indicates lesser risk for exposed population relative to reference population
how do you calculate and interpret odds ratio
odds of the first group/ odds in the seconds grouphow
how do you calculate and interpret relative risk
death or disease risk in a specific population/ risk of people from all other groups
definition of attributable risk
amount of proportion of incidence of disease or death in individuals exposed to a specific risk factor
definition of population attributable risk
risk in the total population that would not have occurred if exposure had not occurred )may also be expressed as number of cases)
PRD = R total - Ru
what type of epi study uses case control sutdies
main features:
- individuals with the outcome are identified (cases)
- individuals without the outcome are identified (controls or referents)
- exposure is determined for cases and controls at an appropriate time IN THE PAST (there is no follow-up)
- the association between exposure and health outcome is quantified using the odds ratio