Measure of Disease Occurrence Flashcards by Kate Guiremand

why measure disease?

know what is going on in a population and how disease is changing it

compare disease in groups

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T/F “risk factor” is another word for “determinant” of disease

true

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epidemiologist are concerned with

presence of existing health problems in a population

occurrence of new health events in a population

and their measurement (quantification)

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what do epidemiologists measure

amount of disease in a population at one point in time or over a period of time

change in amount of disease in a population over a period of time

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stratified=

population subdivided by group (breed, age, sex etc)

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what should be defined when measuring disease occurrence

what is being measured

study population

place of location of study population

time period of study

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study population

subjects of the study

usually a sample from the “source” population

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source population

population from which subjects were drawn

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target population

population to which we may want to generalize our results

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most common types of measurement used

counts
proportions
ratios
rates

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counts

number of animals that have a disease

convey little information on their own

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proportions

count of animals with the disease as a fraction of the total animals that could be diseased

diseased animals/ total in study

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what is the most commonly used proportion in epidemiology

prevalence

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ratios

fraction which the numerator is not part of the denominator

measure of frequency with which an event occurs in a defined population over a specified period of time

expression of the change in the amount of disease in a defined population per unit of time

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what is a commonly used ratio in epidemiology

‘odds’ ratio

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2 types of prevalence

point

period

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2 types of incidence

cumulative incidence

incidence rate

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what is prevalence?

proportion of the study population that is diseased at any one time

amount of disease in the population at any one time

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T/F prevalence provides information about how frequently you might expect to see the condition in your practice

true

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point prevalence

proportion of the study population that is diseased at a single point in time

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what is the most common measurement of prevalence

point prevalence

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how is point prevalence determined

cross-sectional studies

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how do you calculate point prevalence

number of cases of disease in the population at a particular time
——————————————–total population

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what can point prevalence be expressed as

percent
proportion
fraction

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what is period prevalence

proportion of the study population that is diseased during a specified period of time

T/F period prevalence includes old and new cases

true doesnt tell us about when the animals became diseased

T/F period prevalence is the probability that an animal in the study population is diseased during the period of the study

true

how do you calculate period prevalence

number of cases of diseased patients over a period of time -------------------------------------------- total population over that period of time

what is incidence

number of new cases of disease that occur in the study population over time

T/F incidence tells us how frequently non-diseases/susceptible individuals become diseased over time

true

incident cases=

new cases of disease

incidence is interpreted as...

probability of a disease-free animal from the study population becoming diseased risk of becoming diseased

how do you calculate cumulative incidence

number of new cases ------------------------------------------ total population at risk

What is cumulative incidence?

proportion of disease-free (susceptible) individuals in the study population who became diseased during a specified period of time

how is cumulative incidence interpreted

probability (risk) of a susceptible individual in the study population becoming diseased during the study period

how is cumulative incidence expressed

a number | dimensionless

what are the assumptions with cumulative incidence

all individuals in the study pop are at risk of getting the disease of interest every individual in the study pop is assessed at the start of the study entire population must be followed from the start of the study until the end

attack rate

cumulative incidence during an outbreak (specific type of cumulative incidence) applied to a narrowly-defined population

how is attack rate interpreted

probability (risk) of becoming diseased during the course of an outbreak

how do you calculate attack rates

number of new cases ------------------------------------------ total population at risk (exposed)

how is cumulative incidence can be expressed

number dimensionless fraction may not have a reference to time as it is assumed to be the duration of the outbreak

what is incidence rate

instantaneous rate of occurrence of new cases of disease among non-diseased animals in the population

when is incidence rate used

when animals are entering and leaving the population

T/F incidence rate can be easily interpreted at the individual animal level

false

how do you calculate incidence rate

number of new cases ------------------------------------------ sum of the length of time

incidence rate is expressed as

number of cases per animal-time at risk

T/F ONLY the incidence rate is reported as animal-time at risk

true period prevalence and cumulative incidence are reported as cases/animals/time

prevalence vs incidence

prevalence: measure of amount of disease in a population incidence: measure of the rate of disease occurrence

relationship between prevalence and incidence

a new case (incidence case) becomes and old case (prevalent case) and remains so until recovery or death

T/F the prevalence of a disease may increase when incidence remains stable but survival of cases improves

true because reasons

which is used for chronic conditions

prevalence

used to assess causes for disease

incidence

best measure to assess increasing or decreasing trends in disease frequency

incidence

disease risk

probability of becoming diseased

at risk

means individual is not diseased an is capable of becoming diseased

risk factors

factors that increase the probability of becoming diseased

exposure to a risk factor

individual has come into contact with a risk factor or has the risk factor (while not diseased)

mortality rate

incidence of death in a given time period

how to calculate mortality rate

number of deaths during a specified time period ------------------------------------------ total population

case-fatality rate

number of cases of a specific disease that are fatal, within a specific time following disease onset or diagnosis

how to calculate case-fatality rate

No. of cases of disease that die in a specified time period following disease onset ------------------------------------------ total number of individuals with the disease (cases)