BIOL 437 Measures of Risk Flashcards
measures of risk
1. Frequency measures >ratio, proportion, rate 2. Morbidity Frequency Measures >incidence and prevalence >mortality rate
frequency measures
- characterize only part of the distribution
- compare one part to another, or to the entire distribution
ratio
- relative magnitude of two quantities
- comparison of any two values
- numerator and denominator do not need to be related
- used as both descriptive measures and analytic tools
death-to-case ratio
- commonly used
- number of deaths during specific period divided by new cases in same period
- a measure of severity of an illness
proportion
- comparison of a part to the whole
- numerator is included in the denominator
- decimal, fraction or percent
uses of proportions
- used as descriptive measures
- used to describe the amount of a disease that is attributable to a specific exposure
- can be converted to ratios
proportionate mortality
- proportion of deaths in a specifed population during a period of time that are attributable to different causes
- each cause is a percentage of all deaths
rate
- measure of frequency with which an event occurs in a defined population over a specified period of TIME
- measure of risk
types of rates
- incidence rate: how quickly
- attack rate: proportion that develops illness
- prevelance rate: proportion at particular time
- case-fatality rate: die
morbidity
-any departure (subjective or objective) from a state of physiological or psychological well-being
>disease, injury, disability
incidence
-occurence of new cases in a population over specific time
>new cases in a community
>new cases per unit of population
ex. incidence proportion or incidence rate
incidence proportion
- attack rate
- probability of developing a disease (cumulative incidence)
- proportion of initially disease-free that develops disease during specific time
- numerator is is denominator
- used in outbreak setting
types of attack rates
- Overall attack rate
- Food-specific attack rate
- Secondary attack rate
secondary attack rate
-difference between community transmission vs. transmission within a household or closed population
incidence rate
- person-time rate
- incorporates time directly into denominator
- generally applies to long-term cohort follow-up study
- each person is observed from a set starting time until one of four ‘end points’ is reached
end points
- onset of disease
- death
- migration out of study
- end of study
incidence rate is
-ratio of number of cases to the total time the population is at risk of disease
uses of incidence rate
- describes how quickly disease occurs in a population
- accomadates for persons entering and leaving the study
disadvantages of incidence rates
- assumes the probability of disease during the study period is constant
- long-term cohort studies are not very common
prevelance
- sometimes called prevelance rate
- includes all cases, new and pre-existing
point prevelance
-particular point in time
period prevelance
-over an interval of time
prevelance vs. incidence
- prevelance: HAVE condition, all cases regardless when it began
- incidence: DEVELOP condition at a particular time, only NEW cases
prevelance based on
- incidence
- duration of illness
- often a measure of chronic diseases
