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25 Cards in this Set
- Front
- Back
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What is the "equation" for incidence?
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# 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
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What is the definition of incidence?
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Rate of new disease occurring
-Defines a per capita risk of getting disease over a specified period of time |
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What are the 3 part of Step 1 (screening for prevalent cases at baseline) for measuring incidence?
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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 |
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What is step 2 of measuring incidence?
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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 |
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What is the "equation" for incidence rate?
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# 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 |
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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?
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3/ [(10 x 1 year) + (4 x 0.75 years) + (4 x 0.5 years)]=
3/15= 20%/ year |
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What term describes the likelihood of susceptible animals becoming infected over time? What does it measure?
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Incidence- measures transmission
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What is the "equation" for prevalence?
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(# 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) |
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What are the units of prevalence?
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It's a ratio so its unitless
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What are the units of incidence?
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It's a rate so its unit/ time
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What's the prevalence of the disease in January 2004 if the solid lines are diseased animals and dotted are healthy animals?
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3/5
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What was the incidence of disease in 2004 if the solid lines are diseased individuals and the dotted lines are healthy individuals?
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; 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
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What is the risk associated with maintaining infected individuals?
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Have more individuals that are capable of transmitting the disease
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What is the simplified rule of thumb for calculating prevalence if in a closed population?
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Prevalence= Incidence * duration of disease
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If the prevalence of a disease is 20% and you find that animals survive about 5 years, what's the incidence?
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Prevalence=incidence * duration
Incidence= prevalence/ duration Incidence= 0.2/ 5= 4% / year |
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What are 3 problems encountered when trying to measure incidence and prevalence?
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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 |
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What is mortality?
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chances of dying once infected with a disease
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What is the "equation" for annual mortality rate for disease X?
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(total # of deaths in a year due to dz X)/ (# of animals in pop at midyear)
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What is the "equation" for case fatality rate?
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Case fatality rate= (# of animals dying during a specified period of time after disease onset) / (# of individuals w/ specified disease)
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Why do epidemiologic studies have to account for age adjustment?
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Age structure can skew death rate
e.g. if looking at breast cancer then will have higher incidence if an older population |
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How do you account for age adjustment?
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Define age-specific death rates and compare those
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What term defines disease burden in the population?
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Prevalence- represents the likelihood of being a case
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What is the importance of determining mortality rates?
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Allows comparing importance of different diseases in a population
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Case fatality rates inform about ____ of diseases.
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Severity
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When comparing populations, rates may need to be adjusted according to factors such as ____, _____ or _____.
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Age, sex or breed
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