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### 25 Cards in this Set

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 What is the "equation" for incidence? # of NEW cases of a disease occurring in a population during a specified period of time/ # of animals AT RISK of developing the disease during that period What is the definition of incidence? Rate of new disease occurring -Defines a per capita risk of getting disease over a specified period of time What are the 3 part of Step 1 (screening for prevalent cases at baseline) for measuring incidence? 1) Initially identify a population 2) Determine who has the disease and who does not 3) Follow up only those who did not have the disease at baseline What is step 2 of measuring incidence? Follow-up and re-screening at 1 year to identify cases that developed during the year -Follow up only on those people that did not have the disease at baseline What is the "equation" for incidence rate? # of new cases of a disease occurring in a population during a specified period/ # of animal-years-at-risk of developing disease during that period -Same numerator as incidence You are doing research where you monitor 10 pups for 1 year, 4 pups for 9 months and another 4 pups that you observe for 6 months, what is the incidence rate if there was a total of 3 positive cases discovered? 3/ [(10 x 1 year) + (4 x 0.75 years) + (4 x 0.5 years)]= 3/15= 20%/ year What term describes the likelihood of susceptible animals becoming infected over time? What does it measure? Incidence- measures transmission What is the "equation" for prevalence? (# of cases of a disease in a population at a specified point in time)/ (# of animals in the population at that time) = Infected/ (Infected + susceptible + recovered) What are the units of prevalence? It's a ratio so its unitless What are the units of incidence? It's a rate so its unit/ time What's the prevalence of the disease in January 2004 if the solid lines are diseased animals and dotted are healthy animals? 3/5 What was the incidence of disease in 2004 if the solid lines are diseased individuals and the dotted lines are healthy individuals? ; New cases are only the new 2 black lines =2 for numerator; denominator= 2 because only 2 animals were capable of getting NEW disease so incidence =100% for 2004 What is the risk associated with maintaining infected individuals? Have more individuals that are capable of transmitting the disease What is the simplified rule of thumb for calculating prevalence if in a closed population? Prevalence= Incidence * duration of disease If the prevalence of a disease is 20% and you find that animals survive about 5 years, what's the incidence? Prevalence=incidence * duration Incidence= prevalence/ duration Incidence= 0.2/ 5= 4% / year What are 3 problems encountered when trying to measure incidence and prevalence? 1) Defining who has the disease 2) Problems w/ hospital data -Source of a lot of data= not a random sample 3) Problems with denominator -Hard to define total population What is mortality? chances of dying once infected with a disease What is the "equation" for annual mortality rate for disease X? (total # of deaths in a year due to dz X)/ (# of animals in pop at midyear) What is the "equation" for case fatality rate? Case fatality rate= (# of animals dying during a specified period of time after disease onset) / (# of individuals w/ specified disease) Why do epidemiologic studies have to account for age adjustment? Age structure can skew death rate e.g. if looking at breast cancer then will have higher incidence if an older population How do you account for age adjustment? Define age-specific death rates and compare those What term defines disease burden in the population? Prevalence- represents the likelihood of being a case What is the importance of determining mortality rates? Allows comparing importance of different diseases in a population Case fatality rates inform about ____ of diseases. Severity When comparing populations, rates may need to be adjusted according to factors such as ____, _____ or _____. Age, sex or breed