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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 |
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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 |
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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 |
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Rate |
-a ratio that consists of a numerator and a denominator and in which time forms part of the denominator |
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How does a rate differ from a proportion? |
-the denominator for rates involves a measure of time |
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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 |
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What are the elements in rates? |
-disease frequency -unit size of population -time period during which an event occurs |
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Reference Population |
-denominator of a rate -population from which cases of a disease have been taken from |
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Prevalence |
the number of existing cases of a disease or health condition in a population at some designated time |
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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 |
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Period Prevalence |
-total number of cases of a disease that exist during a specified period of time |
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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 |
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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 |
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Three Elements of Incidence |
-numerator = number of new cases -denominator = the population at risk -time = the period during which the cases occur |
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Are individuals who have previously had the disease included in the number of cases when determining incidence? |
no |
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Population at risk may include: |
-those exposed to disease agent -unimmunized -may consist of the entire population |
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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 |
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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 |
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What is the numerator of an AR made up of? |
people who are ill as a result of the exposure to the suspected agent |
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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 |
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Cumulative Incidence |
the proportion of a fixed population that become diseased during a stated period |
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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 |
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What is a requirement of cumulative incidence? |
the disease status must be determined for everyone in the denominator |
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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 |
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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. |
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What is the denominator in incidence density? |
person-time |
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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 |
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The prevalence of a disease is ______ to the incidence rate times the duration of a disease. |
proportional |
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If duration of disease is short and incidence is high, prevalence is ______ to incidence. |
similar |
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If duration of disease is long and incidence is low, prevalence ________ greatly relative to incidence. |
increases |
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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 |
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The basic concepts of rates can be broken down into three groups: |
-crude rates -specific rates -adjusted rates |
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Crude Rate |
summary rates based on the actual number of events over a given time period |
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Crude Birth Rate |
-used to measure the population growth -used as an index to compare developed and developing countries |
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Is crude birth rate higher or lower in less developed countries compared to developed countries? |
higher |
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What is the use of infant mortality rate? |
-international comparisons -a high rate indicates unmet health needs and poor environmental conditions |
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What is fetal death rate used for? |
used to estimate the risk of death of the fetus associated with the stages of gestation |
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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 |
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Neonatal Mortality Rate |
reflects events happening after birth (primarily congenital malformations and prematurity) |
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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 |
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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 |
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Specific Rates |
refer to a particular subgroup of the population defined in terms of race, age, sex, or single cause of death or illness |
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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 |
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Age Specific Rate |
the number of cases per age group of population during a specified time period |
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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 |
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Are specific rates a much better indicator or risk than crude rates? |
yes |
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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 |
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____ is probably the most important variable in risk of morbidity and mortality |
age |
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Two methods of Adjusted Rates |
-direct method -indirect method |
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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 |
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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 |
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Indirect Method |
may be used if age-specific death rates of the population for standardization are unknown or unstable |
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Standardized Mortality Ratio (SMR) |
can be used to evaluate the result of the indirect method |
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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 |