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7 Cards in this Set
- Front
- Back
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3 basic measures of disease occurrence |
1) counting number of cases 2) prevalence 3) incidence |
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Problems w. Counting Cases |
1) *Population size must stay constant 2) *Constant fraction of population must be sampled 3) Clinical submissions are always biased--submitting b/c disease is suspected and does not reflect the general population 4) Protocols can vary state to state |
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Prevalence |
-Proportion of the population that has the disease at one specific point in time -Measures existence of disease, is index of the probability of being a case -Depends on 1) rate of disease onset 2) rate of recovery Prevalence = (#existing cases at a given time)/(total population at risk at a given time) Prevalence = (incidence) x (duration) |
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Prevalence can be used to... |
-compare populations over time -compare populations in different places -compare populations under different conditions |
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Problems with Prevalence |
1) almost always varies depending on signalment (age, sex, breed, use of animals) 2) not a pure measure of disease occurrence b/c it depends on rate of disease onset AND RECOVERY RATE--always have animals that are in the recovery phase and who do not represent new cases |
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Ways to Report Prevalence |
1) specific measure 2) adjusted measure |
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Incidence |
-instantaneous per capita rate of disease onset -measure appearance of disease, is an index of of the probability of becoming a case incidence rate = i = -dR/dt (1/R) "true incidence" = (the rate of change in R) / (#animals at risk) R=# of animals at risk of disease i=1/(average age at disease onset) -if "true incidence" is high there is a greater risk of acquiring the disease and the average age of disease onset is low |
