02 Measures of frequency Flashcards
What is a disease?
- opposite of health
- combination of symptoms, signs & test -> diagnosis
health is a state of complete physical, mental and social well-being
What is a case?
- person that has disease of interest
- inclusion/exclusion criteria -> threshold can alter frequency
What describes a population?
- age
- sex
- socio-demographics
What are typical measures for time and place?
- region/country
- seasonal, secular trends
Define attack rate
- used in outbreaks with short incubation time
attack rate = (exposed & ill) / exposed
- more a rate
- time must be stated
What is the difference between fixed and open populations?
fixed:
- based on one event
- permanent
- no gain of new members
open:
- based on condition
- membership is transitory
Population at risk
- part of population that has risk for disease
- possibility to move from denominator to numerator
- case / population at risk
Steps to measure the frequency of a disease (summary)
- define and count cases (persons with disease)
- define and count population (persons at risk)
- define time frame
Incidence vs. prevalence
Prevalence:
- existing cases (what portion of population is sick?)
Incidence:
- occurrence of new cases (how quickly are people catching the disease?)
What is the cumulative incidence?
- fixed population
- incidence proportion
- new cases that accumulate during time period
new cases in period / population at risk at start of period
What is the incidence density rate?
- open population
- person-time at risk instead of population at risk
new cases in period / person-time at risk
What means point prevalence?
- measured per 100 persons
- at certain time point
people with disease at time point / population at time point
What means period prevalence?
- measured per 100 persons
- over period
people with disease in period / average population in period
Mortality vs. lethality
Mortality:
- deaths per population
Lethality:
- deaths per patients
