Lecture 3 Flashcards
What measures do we use to track a population’s health?
Risk factors: Prevalence
Morbidity: disease incidence, disease prevalence, medical care usage
Mortality: total and cause-specific
What are the sources of morbidity data?
Health data systems disease registries surveillance systems medication/device sales surveys research studies
Proportion
Division of two numbers where the numerator is a subset of denominator
Rate
A proportion where time is always in deominator
How do you measure burden of disease?
Proportions - Number affected / total population
How do you measure risk of disease?
Rates - events / population-time
Incidence
number of new disease events
Incidence rate
rate at which new diseases are occurring
Cumulative incidence
cumulative risk for developing new disease among persons over some period of time
Incidence rate per 1000
Number of new cases of a disease occurring in the population during a specified interval of time / number of persons at risk of developing the disease during that interval of time X 1000
Person-years
(# of subjects) x (years of follow-up per subject)
Prevalence per 1000
Number of cases of disease present in the population at a specified time / Number of persons in the population at that specified time X 1000
What are the types of prevalence?
Point prevalence
Period prevalence
Cumulative incidence (proportion)
Number of new cases of a disease occurring in a population during a specified period of time / Number of person at risk for the disease during that period of time
What are estimates of risk?
Incidence rate and Cumulative incidence
When is cumulative incidence used commonly?
Period of time = lifetime
Prevalence = Incidence x Duration
Higher incidence results in higher prevalence
Longer duration results in higher prevalence
What decreases prevalence?
Deaths
Cures
Incidence and prevalence for pancreatic cancer
Incidence low
Duration short
Prevalence low
Incidence and prevalence for common cold
Incidence high
Duration short
Prevalence low
Incidence and prevalence for chronic lung disease
Incidence low
Duration long
Prevalence high
Incidence and prevalence for hypertension
Incidence high
Duration long
Prevalence high
Factors that increase observed prevalence
Increase in new cases
Longer duration of the disease
Prolongation of life of patient withoutcure
Improved diagnostic facilities (better reporting)
In-migration of cases
Out-migration of healthy people
Factors that decrease observed prevalence
Decrease in new cases Shorter duration of disease High case-fatality from disease Improved proportion cases cured In-migration of healthy people Out-migration of cases
What are the problems with numerators and denominators
Strict criteria to define both
Numerator must come from denominator
All in the denominator must be able to go into the numerator
What are the variability in defining disease?
Level of illness (sick, disabled, etc) Specific illness (diagnosis)
What are the variability in methods of ascertainment?
Using regularly available data (disease reporting, review of medical records)
Using specially planned data collection (interviews, direct examinations)
What are the issues related to identifying cases?
Variability in defining disease
Variability in methods of ascertainment
How could we measure the prevalence of childhood asthma?
questionnaire, physiological measures, medical records
“Do you currently have asthma?”
Example of point prevalence
“Have you had asthma during the n years?”
Example of period prevalence
“Have you ever had asthma?”
Example of cumulative or life-time incidence
Limitations of Surveys: Characterizing disease by asking questions
- widely used to describe population health
- depend on access to care
- depend on recall
- subject to bias (limited recall, lack of knowledge, interviewer/informant)
Errors in classifying numerators
- bias and variation in self-reporting
- variation in disease classification
- errors in administrative data bases/medical records (coding for billing purposes, temporal changes, incomplete information, legibility)
Problems with denominator
- characterizing the population
- defining the population at risk
Major uses of cumulative incidence
Research on causes, prevention, and treatment of disease
Major uses of incidence rate
Research on causes, prevention, and treatment of disease
Major uses of prevalence
Resource planning
