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25 Cards in this Set
- Front
- Back
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Proportion
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- expression of probability in which the numerator is derived from the denominator
- prevalence |
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prevalence
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- the probability that disease is present at a particular point in time
= incidence rate x avg duration of disease |
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true rate
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a proportion (as stated above) which includes a period of time
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incidence rate
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- The rate of the development of disease (disease diagnosis) over the period of a year
= prevalence/avg duration |
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Rates
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- to describe the epidemiology of disease
1.) Incidence rate 2.) Prevalence 3.) Case fatality |
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Case fatality
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the probability of dying once the disease has developed
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Mortality rate
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- the incidence of death per 100,000 people per year
= incidence rate x case fatality |
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Obtaining rates: data sources
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1.) Complete data from total population: mortality rates
2.) Incomplete data from total population: reportable diseases 3.) Representative sample of the total population: random sampling 4.) Non-representative sample of the total population: convenience sample or data from sentinel site |
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Comparing rates
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1.) Subtraction
2.) Rate ratio |
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Rate ratio
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- Relative probability of events in one population compared to another
- This population comparison is a group association and is not capable of establishing an association at the individual level |
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Central limit theorem
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- If many random samples are obtained, estimates calculated from those samples, on average, will be the same as the measurement in the original population
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Standard error
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- a measure of the size of the sampling error
- The dispersion (spread) in the mean that would be if ALL possible samples of the same size as the one actually obtained were drawn from the population |
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Standardization
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An adjustment for factors already known to affect a particular rate
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Indirect method
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A comparison of the observed number of events in the sample of interest to the number expected if the sample had the same age distribution as the general population
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Standardized mortality ratio =
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= observed number of deaths/expected number of deaths
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Healthy worker effect
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- standardized mortality ratio = <1
- due to the tendency of a specific population - if “1” …. possibly a dangerous job |
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Direct Method
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- To compare two groups in a population
- To examine changes over time in a population |
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Artifactual differences
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- Not a true difference
- A change in incidence rate, prevalence, or case fatality may be due to the WAY a disease is: 1) measured 2) detected/recognized 3) defined |
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True differences
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- real differences which can influence rates
1.) Unpredictable random variation 2.) Exhausting the denominator 3.) Cohort effect |
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Unpredictable random variation
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- Statistically a rare (unusual) event
- regression to the mean - Rare events are unlikely to recur by chance - Measurements subsequent to an unusual measurement are likey to be close to the mean |
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Exhausting the denominator
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A reduction in the size of the at-risk group
- eg. Hemophiliacs exposed to HIV |
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Cohort effect
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A group shares a common exposure
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Comparison of rates
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- cause and effect is NOT implied
- group association |
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Life expectancy
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- The average number of years of remaining life from a given age, usually stated as life expectancy at birth
- Based on probabilities of death in each age group in a given year - Assumptions: The population is stationary and Age-specific probabilities of death in each subsequent year remain the same Life expectancy at birth is the average number of years of remaining life for an individual born into a stationary population |
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Summary measurement
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- Combines the mortality rates for each year of age in a population for a particular year
- Mortality rates: Census and death records |
