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14 Cards in this Set

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Attack Rate
# ppl at risk in whom a certain illness develops / total number of people at risk

* useful for comparing the risk of disease in groups with different exposures
Incidence
# new cases of disease occurring in the pop'n during a specified period of time / # people at risk of developing the disease during that periodof time
Cumulative Incidence
# new cases of disease in pop'n at risk during a specified period of time / # people at risk for developing the disease at BEGINNING of time period

* estimates the risk of a new outcome in a given time period

* proportion
Incidence Density
* # new cases of disease in pop'n at risk during a specified period of time / person-years at risk for disease

* person-years: sum of the different times that each individual was at risk

* rate
Prevalence
# cases WITH DISEASE in a pop'n at a specific time / total pop'n at that time

* snapshot of presence of disease (existing + new cases) in a pop'n at a given time

* measures the burden of disease in a community

* not a measure of risk
Point Prevalence
prevalence of a disease at a point in time

ex. "Do you currently have asthma?"
Period Prevalence
prevalence of a disease during a certain period

every person in the numerator had the disease at some time during the period specified
- not concerned with when disease developed or how long it persisted

ex. "Have you had asthma during the last 5 years?"
Relationship between Incidence and Prevalence
Prevalence = Incidence x Duration

* duration is determined by death or treatment
Increasing and Decreasing Prevalence
Increase:
- addition of new cases (incidence)
- new measure that enhances survival or better detects the disease

Decrease:
- cures & deaths (reduce # of diseased ppl in pop'n)
Examples of Prevalence = Incidence * Duration
1) rapid cure or death
- prevalence ≈ incidence
- short duration

2) chronic disease (diabetes)
- ↑ prevalence
- long duration & low incidence

3) Acute, short duration disease (strep throat)
- ↑ prevalence and ↓ incidence
Annual Mortality Rate
total # deaths from all causes in one year / # persons in the pop'n at midyear

* anyone in the denominator must be able to enter the numerator
- denominator include those who have the disease and those who don't have it but are at risk

* be mindful that popn's can differ in regard to many characteristics that affect mortality
Specific Rate
placing a restriction on both the numerator and the denominator

Ex. age-specifc mortality rate

# deaths from all causes in one year in children younger than 10 years old / # children in the pop'n younger than 10 years old at midyear

Ex. cause-specific rate

# deaths from lung cancer in one year / # persons in the pop'n at midyear
Case-Fatality Rate
# individuals dying during a specified period of time after disease onset or diagnosis / # individuals with the specified disease

denominator limited to those who already have the disease

* what PERCENTAGE of people diagnosed with a certain disease die within a certain time after diagnosis

* measure of the severity of the disease
Proportionate Mortality
# deaths from disease X in the U.S. in 1999 / total # deaths in the U.S. in 1999

* what PROPORTION from all deaths was caused by disease X

* does not tell us the risk of dying from a disease