Measuring the Occurrence of Disease Flashcards
What does epidemiology mean?
It is the study of the distribution and determinants of health related events/states in specified populations, and the application of this study to the control of health problems.
The cornerstone of epidemiology is knowing the person, place, and time.
Why do we measure occurrence of disease?
To allow for easier planning (resources, access to health care, how are disease patterns changing?)
What is an epidemic?
A disease where rate increases above baseline levels
What are the types of measures used in epidemiology?
Count: Numerator only (number of people with x)
Ratio: Numerator and Denominator (number of still-births per 1000 live-births)
Proportion: Special type of ratio (numerator contained in denominator)
Rate: Ratio that involves time (Number of colds per 1000 primary students per year)
What are the types of populations in epidemiology?
Closed and open populations.
Closed populations are defined by specific event so no new members. (Eg. atomic bomb survivors born in 1920 in Hiroshima) the population loses members only through death over time.
Open populations are dynamic populations which add members through birth and lose members through death and emigration
What is prevalence?
Total number of cases in a given population at a specific point in time. (Total number of cases/total population at a point in time)
What factors influence prevalence?
Diagnostic criteria
Awareness
Access to healthcare
Birth rate
Migration
Cure
Prolonging life but no cure
Death
What is the difference between point and period prevalence?
Point prevalence: Occurrence of disease at a specific point in time
Period prevalence: Occurrence of disease within a defined period of time
What is incidence?
Number of NEW cases of a disease occurring during a specified time in a population at risk for developing the disease.
What are the types of incidence measures?
Cumulative incidence (incidence proportion or ‘risk’)
Incidence rate (Incidence density)
What are the criteria for a person to be at risk of a disease?
When they are alive
When they are able to get the disease
When they do not already have the disease
What does cumulative incidence refer to?
Number of new cases/total population at risk
This proportion is during a specified period of time.
What is incidence rate?
The numerator is the number of new cases in the population over a time period.
But the denominator is the sum of each individuals time at risk
I.e Number of events per person-time
How is risk of Person-Years calculated?
Years per person prior to having the disease while still being at risk.
What is the numerator and denominator for incidence?
Numerator: New cases occuring during given time period
Denominator: Number of person-years free of the disease of interest. Number of people free of disease at baseline
