Epidemiologic Data Measurements Flashcards
- Disease, injury, or death can be measured in different ways.
- It can be related to different denominators, depending on the purpose of the research and the availability of data.
- It depends on the purpose of the research.
Frequency
- The number of persons in a defined population who have a specified disease or condition at a given point in time.
- Existing Cases
Prevalence
- Specific to the day or time.
- Includes all existing cases.
Point Prevalence
- Over a time period.
- Includes all existing + new cases.
Period Prevalence
- Prevalence is commonly illustrated using a bar graph.
Graph Representation
- Refers to new cases in a specific time period.
- Tracks the frequency of occurrence of disease, injury, or death that marks transitions:
- From well to ill.
- From uninjured to injured.
- From alive to death.
Incidence
Two Measures of Incidence:
Risk and Rate
- Related to the population at risk at the beginning of the study period.
- The proportion of individuals in a population (initially free of disease) who develop the disease within a specific time interval.
Risk
- A more precise measure of the population at risk during the study period.
- Measured in person-time units.
- Measures the frequency of new cases.
Rate
- Refers to the outcomes of the disease:
- Either the individual died or recovered from the disease.
Morbidity
- Sensitivity measures the proportion of people who test positive among all those who actually have the disease.
Sensitivity
Specificity measures the proportion of people who test negative among all those who do not have the disease.
Specificity
Indicates how likely it is that a patient truly has the disease if the test result is positive.
Positive Predictive Value (PPV)
Indicates how likely it is that a patient truly does not have the disease if the test result is negative.
Negative Predictive Value (NPV)
it is directly related to prevalence
PPV
As prevalence decreases, PPV decreases due to more false positives.
PPV
Indicates how likely it is that a patient truly does not have the disease if the test result is negative.
Negative Predictive Value (NPV)
inversely related to prevalence
NPV
As prevalence decreases, NPV increases due to fewer false negatives.
NPV
Defined as the proportion of persons who are unaffected at the beginning of a study period but experience a risk event during the study perio
RISK
May include death, disease, or injury.
Risk Event
The denominator includes all individuals at risk at the beginning of the study period.
RISK Cohort
Refers to the number of events that occur in a defined time period, divided by the average number of people at risk for the event during the study period.
RATE
Compares two numbers, often expressed as “1:9”.
RATIO
Refers to the fraction of a population experiencing a specific event.
PROPORTION
