MEASURES IN EPIDEMIOLOGY EXAM
QUESTION WITH CORRECT ANSWERS
Co-primaries - ANSWER-Cases so closely in time to index case that they are
considered index cases
Initial Cases - ANSWER-Calculated by index + Co-primaries
Index Cases - ANSWER-Cases that first come to the attention of public health
authorities.
Case Fatality Rate - ANSWER-Number of deaths caused by a disease among those
who have disease. Examples of diseases with a high CFR are rabies and
meningococcal meningitis. Calculated by (# of deaths due to disease)/(# of cases of
disease)
Prevalence - ANSWER-Number of existing cases of a disease or health condition in a
population. Includes both new and pre-existing cases. Describes the burden of a health
problem and estimates frequency of exposure. Can be used to determine allocation of
health resources. There are two different types: Point Prevalence and Period
Prevalence. Not a measure of risk. Based on incidence and duration. Often used for
chronic diseases which have a long duration and dates of onset that are difficult to
pinpoint.
Point Prevalence - ANSWER-Calculated by (# of persons ill)/(Total Number in the
Group) at a point of time
Period Prevalence - ANSWER-Calculated by (Number of Persons Ill)/(Average
Population) during a time period
Interrelationship between Incidence and Prevalence - ANSWER-If duration is short and
incidence is high, prevalence becomes similar to incidence(an example of this is the
common cold). If duration of disease is long and and incidence is low, prevalence
increases greatly relative to incidence(ex. many chronic diseases). The prevalence of a
disease is proportional to the incidence rate times the duration of a disease.
Factors that Cause Prevalence to Increase - ANSWER-increase in incidence, longer
duration of the case, in-migration of cases, prolongation of life of patients without a cure,
out-migration of healthy people, in-migration of susceptible people, and improved
diagnostic facilities(better reporting)
Factors that Cause Prevalence to Decrease - ANSWER-Decrease in incidence, shorter
duration of disease, in-migration of healthy people, improved cure rate, high-case
fatality rate, out-migration of cases
, Mortality Rate(Crude Death Rate) - ANSWER-Measure of the frequency of occurrence
of death in a population of death in a population during a specific time period.
Calculated by (number of deaths in a year)/(Reference Population during the midpoint
of the year)
Case-Fatality Rate - ANSWER-Measure of Risk. The proportion of persons with a
particular condition(cases) who die from that condition. Calculated by (number of cause
specific deaths among the incident cases)/(number of incident cases).
Crude Birth Rate - ANSWER-Used to project population changes, it is affected by the
number and age composition of women of childbearing age. Calculated by (# of live
births within a given period)/(population size at the middle of that time period)
General Fertility Rate - ANSWER-Used for comparisons of fertility among race, age,
and socioeconomic groups. Calculated by (# of live births within a year)/(# of women
aged 15-44 years during the midpoint of that year)
Infant Mortality Rate - ANSWER-Used for international comparisons; a high rate
indicates unmet health needs and poor environmental conditions. Calculated by (# of
infant deaths among first year of life during the year)/(# of live births during the year)
Fetal Death Rate - ANSWER-Used to estimate the risk of death of the fetus associated
with the stages of gestation. Calculated by (number of fetal deaths after 20 weeks or
more)/(Number of live births + Number of fetal deaths after 20 weeks or more). Late
fetal death is calculated by (number of fetal deaths after 28 weeks or more)/(number of
live births + number of fetal deaths after 28 weeks or more).
Neonatal Mortality Rate - ANSWER-Reflects events happening after birth such as
malformation, premature, and low birth weights. Calculated by (number of infant deaths
under 28 days of age)/(number of live births)
Post-neonatal Mortality Rate - ANSWER-Reflects environmental events, control of
infecctious diseases, and nutrition. Calculated by (# of infant deaths from 28 days to
365 days after birth)/(# of live births-neonatal deaths)
Perinatal Mortality Rate - ANSWER-Reflects environmental events that occur during
prengnacy and after birth; it combines mortality during the prenatal and postnantal
periods. Calculated by (number of late fetal deaths after 28 weeks or more gestation
plus infant deaths within 7 days)/(Number of live births + Number of late fetal deaths)
Maternal Mortality Rate - ANSWER-Reflects health care access and socioeconomic
factors; it includes maternal deaths resulting from causes associated with pregnancy
and puerperium(during and after birth). Calculated by (# of deaths assigned to causes
related to childbirth)/(# of live births)
QUESTION WITH CORRECT ANSWERS
Co-primaries - ANSWER-Cases so closely in time to index case that they are
considered index cases
Initial Cases - ANSWER-Calculated by index + Co-primaries
Index Cases - ANSWER-Cases that first come to the attention of public health
authorities.
Case Fatality Rate - ANSWER-Number of deaths caused by a disease among those
who have disease. Examples of diseases with a high CFR are rabies and
meningococcal meningitis. Calculated by (# of deaths due to disease)/(# of cases of
disease)
Prevalence - ANSWER-Number of existing cases of a disease or health condition in a
population. Includes both new and pre-existing cases. Describes the burden of a health
problem and estimates frequency of exposure. Can be used to determine allocation of
health resources. There are two different types: Point Prevalence and Period
Prevalence. Not a measure of risk. Based on incidence and duration. Often used for
chronic diseases which have a long duration and dates of onset that are difficult to
pinpoint.
Point Prevalence - ANSWER-Calculated by (# of persons ill)/(Total Number in the
Group) at a point of time
Period Prevalence - ANSWER-Calculated by (Number of Persons Ill)/(Average
Population) during a time period
Interrelationship between Incidence and Prevalence - ANSWER-If duration is short and
incidence is high, prevalence becomes similar to incidence(an example of this is the
common cold). If duration of disease is long and and incidence is low, prevalence
increases greatly relative to incidence(ex. many chronic diseases). The prevalence of a
disease is proportional to the incidence rate times the duration of a disease.
Factors that Cause Prevalence to Increase - ANSWER-increase in incidence, longer
duration of the case, in-migration of cases, prolongation of life of patients without a cure,
out-migration of healthy people, in-migration of susceptible people, and improved
diagnostic facilities(better reporting)
Factors that Cause Prevalence to Decrease - ANSWER-Decrease in incidence, shorter
duration of disease, in-migration of healthy people, improved cure rate, high-case
fatality rate, out-migration of cases
, Mortality Rate(Crude Death Rate) - ANSWER-Measure of the frequency of occurrence
of death in a population of death in a population during a specific time period.
Calculated by (number of deaths in a year)/(Reference Population during the midpoint
of the year)
Case-Fatality Rate - ANSWER-Measure of Risk. The proportion of persons with a
particular condition(cases) who die from that condition. Calculated by (number of cause
specific deaths among the incident cases)/(number of incident cases).
Crude Birth Rate - ANSWER-Used to project population changes, it is affected by the
number and age composition of women of childbearing age. Calculated by (# of live
births within a given period)/(population size at the middle of that time period)
General Fertility Rate - ANSWER-Used for comparisons of fertility among race, age,
and socioeconomic groups. Calculated by (# of live births within a year)/(# of women
aged 15-44 years during the midpoint of that year)
Infant Mortality Rate - ANSWER-Used for international comparisons; a high rate
indicates unmet health needs and poor environmental conditions. Calculated by (# of
infant deaths among first year of life during the year)/(# of live births during the year)
Fetal Death Rate - ANSWER-Used to estimate the risk of death of the fetus associated
with the stages of gestation. Calculated by (number of fetal deaths after 20 weeks or
more)/(Number of live births + Number of fetal deaths after 20 weeks or more). Late
fetal death is calculated by (number of fetal deaths after 28 weeks or more)/(number of
live births + number of fetal deaths after 28 weeks or more).
Neonatal Mortality Rate - ANSWER-Reflects events happening after birth such as
malformation, premature, and low birth weights. Calculated by (number of infant deaths
under 28 days of age)/(number of live births)
Post-neonatal Mortality Rate - ANSWER-Reflects environmental events, control of
infecctious diseases, and nutrition. Calculated by (# of infant deaths from 28 days to
365 days after birth)/(# of live births-neonatal deaths)
Perinatal Mortality Rate - ANSWER-Reflects environmental events that occur during
prengnacy and after birth; it combines mortality during the prenatal and postnantal
periods. Calculated by (number of late fetal deaths after 28 weeks or more gestation
plus infant deaths within 7 days)/(Number of live births + Number of late fetal deaths)
Maternal Mortality Rate - ANSWER-Reflects health care access and socioeconomic
factors; it includes maternal deaths resulting from causes associated with pregnancy
and puerperium(during and after birth). Calculated by (# of deaths assigned to causes
related to childbirth)/(# of live births)
