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54 Cards in this Set

  • Front
  • Back

Count

-simplest and most frequently performed quantitative measure in epidemiology


-refers to the number of cases of a disease or other health phenomenon being studied

Ratio

-defined as the value obtained by dividing one quantity by another


-proportions, rates, and percentages are also ratio


-consists of a numerator and denominator

Proportion

-a type of ratio in which the numerator is part of the denominator


-it is important to know the size of the denominator


-may be expressed as a percentage


-states a count relative to the size of the group


-can demonstrate the magnitude of a problem

Rate

-a ratio that consists of a numerator and a denominator and in which time forms part of the denominator

How does a rate differ from a proportion?

-the denominator for rates involves a measure of time

What does the numerator and denominator represent in a rate?

-numerator consists of the frequency of a disease over a specified period of time


-denominator is a unit size of the population

What are the elements in rates?

-disease frequency


-unit size of population


-time period during which an event occurs

Reference Population

-denominator of a rate


-population from which cases of a disease have been taken from

Prevalence

the number of existing cases of a disease or health condition in a population at some designated time

Uses of Prevalence

-provides an indication of the extent of a health problem


-estimates the frequency of an exposure


-determines allocation of health resources such as facilities and personnel

Period Prevalence

-total number of cases of a disease that exist during a specified period of time

How do you determine period prevalence?

combine the number of existing cases at the beginning of the time interval with the new cases that occur during the interval and divide by the average population

Incidence

-the number of new cases of a disease that occur in a group during a certain period of time


-describes the rate of development of a disease in a group over a certain time period

Three Elements of Incidence

-numerator = number of new cases


-denominator = the population at risk


-time = the period during which the cases occur

Are individuals who have previously had the disease included in the number of cases when determining incidence?

no

Population at risk may include:

-those exposed to disease agent


-unimmunized


-may consist of the entire population

What are applications of incidence data?

-help in research on the etiology/causality of disease


-used to estimate the risk of developing a disease and the effects of exposure to a hypothesized factor of interest

Attack Rate (AR)

-alternative form of incidence rate


-used for diseases observed in a population for a short period of time


-often as a result of specific exposure

What is the numerator of an AR made up of?

people who are ill as a result of the exposure to the suspected agent

What is the denominator of an AR made up of?

all people, whether well or ill, who were exposed to the agent during a period of time

Cumulative Incidence

the proportion of a fixed population that become diseased during a stated period

What are two guidelines since the population in cumulative incidence is fixed?

-no one is allowed to enter the denominator after the start of the observation


-numerator can include only individuals who were members of that fixed population

What is a requirement of cumulative incidence?

the disease status must be determined for everyone in the denominator

Why is cumulative incidence hard to calculate?

-most of the regions we live and work in contain dynamic population


-leads to loss of follow up

Incidence Density

-an incidence measure used when members of a population or study group are under observation for different lengths of time


-different length of time due to death, drop out, migration, etc.

What is the denominator in incidence density?

person-time

How you you derive person-years?

summing up the product of each category of length of observation and the number of subjects in the category

The prevalence of a disease is ______ to the incidence rate times the duration of a disease.

proportional

If duration of disease is short and incidence is high, prevalence is ______ to incidence.

similar

If duration of disease is long and incidence is low, prevalence ________ greatly relative to incidence.

increases

What are applications of incidence data?

-help in research on the etiology/causality of disease


-used to estimate the risk of developing a disease and the effects of exposure to a hypothesized factor of interest

The basic concepts of rates can be broken down into three groups:

-crude rates


-specific rates


-adjusted rates

Crude Rate

summary rates based on the actual number of events over a given time period

Crude Birth Rate

-used to measure the population growth


-used as an index to compare developed and developing countries

Is crude birth rate higher or lower in less developed countries compared to developed countries?

higher

What is the use of infant mortality rate?

-international comparisons


-a high rate indicates unmet health needs and poor environmental conditions

What is fetal death rate used for?

used to estimate the risk of death of the fetus associated with the stages of gestation

Fetal Death Ratio

refers to the number of fetal deaths after gestation of 20 weeks or more divided by the number of live births during a year

Neonatal Mortality Rate

reflects events happening after birth


(primarily congenital malformations and prematurity)

Maternal Mortality Rate

-reflects health care access and socioeconomic factors


-includes maternal deaths resulting from causes associated with puerperium (period after childbirth), eclampsia, and hemorrhage

Observed differences in crude rates may be caused by what?

systematic factors (e.g., sex or age distributions) within the population rather than true variation in rates

Specific Rates

refer to a particular subgroup of the population defined in terms of race, age, sex, or single cause of death or illness

10 Leading Causes of Death 25-34 Years, All Races, Both Sexes in US

1. accidents (unintentional injuries)


2. intentional self-harm (suicide)


3. assault (homicide)


4. malignant neoplasms


5. diseases of the heart


6. HIV disease


7. diabetes mellitus


8. cerebrovascular diseases


9. congenital malformations


10. influenza and pneumonia

Age Specific Rate

the number of cases per age group of population during a specified time period

How do you calculate age specific rate?

-stratify population into age groups


-defined by 5 year or 10 year interval


-divide the frequency of the disease in a particular age stratum by the total number of persons within that age group

Are specific rates a much better indicator or risk than crude rates?

yes

Adjusted Rates

summary measures of the rate of morbidity and mortality in a population in which statistical procedures have been applied to remove the effect of differences in composition of various populations

____ is probably the most important variable in risk of morbidity and mortality

age

Two methods of Adjusted Rates

-direct method


-indirect method

Direct Method

may be used if age-specific death rate in a population to be standardized are known and a suitable standard population is available

What is the benefit of standardizing observed rates of disease in the population?

any observed difference that remain are not due to factors such as age, race, or sex

Indirect Method

may be used if age-specific death rates of the population for standardization are unknown or unstable

Standardized Mortality Ratio (SMR)

can be used to evaluate the result of the indirect method

How do you interpret the SMR?

-if the observed and expected numbers are the same, the SMR would be 1.0, indicating that observed mortality is not unusual


-an SMR of 2.0 means that the death rate in the study population is two times greater than expected