Term
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Definition
Ratio: practically of no use
Proportion: of limited use
cRate: of extreme importance and application |
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Term
| Necessities to express a rate |
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Definition
Numerator
Denominator
Time period
Location |
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Term
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Definition
| The number of new cases of a disease divided by the number at risk for the disease, over a given time period |
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Term
| Cumulative Incidence (Risk Rate) |
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Definition
| When the entire population at risk is observed throughout a defined time period |
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Term
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Definition
| When the entire population at risk is NOT observed throughout the entire defined time period |
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Term
| Cumulative Incidence Equation (with no adjustment for withdrawls) |
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Definition
number of new cases
initial number in population |
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Term
| Cumulative Incidence Rate (with adjustment for withdrawls) |
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Definition
number of new cases
initial NAR- 1/2 withdrawls
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Term
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Definition
number of new cases
animal time
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Term
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Definition
number of new cases
(ave.# at risk)*(ETC)
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Term
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Definition
| This special form of risk rate, in which there is a limited period of risk |
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Term
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Definition
number ill
number of total population in reference unit
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Term
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Definition
This is a measure in which the numerator consists of the number of cases of a disease which occurs within the same reference unit following the occurrence of a first, or primary, case.
For diseases conferring prolonged immunity, the denominator in a secondary attack rate usually excludes animals or persons who have previously had the disease.
It is a measure of agent infectivity.
Assumption – secondary cases caught the disease from the primary cases.
Important in propagated outbreaks |
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Term
| Secondary Attack Rate Equation |
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Definition
number of new cases*10
true population at risk
true population at risk= total population - primary cases
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Term
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Definition
This is not a true rate or a risk rate, but a proportion.
Prevalence rates are a measure of all (not just new) cases present at a given time in the given reference population |
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Term
| Overall Death Rate Equation |
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Definition
reported deaths
mean population
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Term
| Factors Affecting Interpretation of Incidence and Prevalence |
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Definition
1. Temporal sequence
2. Disease duration
3. Relationship among incidence, prevalence, and duration of disease
4. True vs. Apparent prevalence
5. Case definition
6. Dangling numerators
7. Population at risk
8. Crude vs. adjusted rates |
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Term
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Definition
apparent prevalence + specificity - 100%
sensitivity + specificity - 100%
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Term
| Standardized Morbidity Rate Equations |
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Definition
observed rate
expected rate
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Term
| Standardized Morbidity Ratio Comparisons |
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Definition
Allow for comparison between the sample population and the standard
Ratio of rates (or counts) that has been adjusted to the sample population
You cannot compare the ratios between populations |
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