Lecture 4 (7/13/16) Flashcards
Mortality indices
mortality rates case fatality proportionate mortality problems with mortality data comparing mortality rates
Mortality rates - deonominator
rates usually calculated on an annual basis
midpoint popuation used = assume all ppl observed for 1 year
midpoint population = # of person-years
Person-time in the Annual Mortality Rate
Number of persons in the population at mid year = Number of persons in the population at midyear x 1 year
What adds people to the denominator of midpoint population?
Births
Immigrants
What remove people from denominator of midpoint population?
Deaths
Emigrants
Annual Mortality Rate from all causes per 1000 population
Total number of deaths from all causes in 1 year / Number of peersons in the population at midyear x 1 year x 1000
What types of mortality rates can you calculate?
all causes, specific causes, total population, population subgroups, exposure subgroups
Cause-specific mortality rate
ex. lung cancer # of deaths from lung cancer per year / # of persons in population at mid year x 1 year x 1000
Case Fatality
‘Rate’ is a proportion
Percent of persons with a disease who die from that disease
# individuals dying during a specified period of time after disease onset/diagnosis / # individuals with specified disease
Artifactual differences in case fatality
statistical sampling
surveillance/reporting bias
Real differences in case fatality
Comorbidity
Differential pathogenicity
Population differences in susceptibility
When is a mortality rate a good index of an incidence rate?
When the case-fatality is high
When duration of the disease is short
Proportionate Mortality
- is a PROPORTION
Percent of deaths due to a specific cause of death
# of deaths due to specific cause / total # of deaths
What is age-adjustment?
A technique for standardizing rates from different populations to the structure of one, common population
Direct age-adjustment
data needed from study pop: age-specific death rates
age-specific rates from: study population
population structure from: standard population
comparison of: age-adjusted rates
Indirect age-adjustment
data needed from study pop: age-structure, total death
age-spefici rates from: standard population
population structure from: study population
comparison of: standardized mortality ratio (SMR)
Standardized Mortality Rate (SMR)
observed # of deaths per year / expected # of deaths per year
Advantages & Disadvantages of Crude Rates
Advantages:
actual summary rates - “observed events”
readily calculable for international studies (widely used despite limitations)
Disadvantages
- since populations vary in composition (e.g. age), differences in crude rates are difficult to interpret
Advantages & Disadvantages of Specific Rates
Advantages:
- homogenous subgroups
- detailed rates useful for epidemiologic and public health purposes
Disadvantages:
- since populations vary in composition (e.g. age), differences in crude rates are difficult to interpret
Advantages & Disadvantages of Adjusted Rates
Advantages:
-represent summary statements
- differences in composition of groups “removed” permitting unbiased comparisons
Disadvantages
- fictional rates - not “real” events
- absolute magnitude dependent on standard population chosen
- opposing trends in subgroups masked
Differences between prevalence and incidence
- prevalence is a proportion, incidence is a rate
- incidence measures new cases while prevalence measures any existing cases
- denominator incidence is persons at risk (healthy, non-diseased) while denominator for prevalence is the total population (including both sick and healthy)
Differences between incidence and cumulative incidence
- incidence rate is a RATE, cumulative incidence is a PROPORTION
- both measure new cases and indicate risk
- time is handled different. time is integral part of denominator for incidence (calculate rates), but not for cumulative incidence (time interval simply referenced)
Classifying causes of death
death certificates
ICD
