Descriptive Epidemiology (ch. 5 and 6) Flashcards
Define denominator.
The population: a group of people with a common characteristic; populations determine who is at risk.
WHO’s definition of health:
physical, mental, and social well-being
How can we define populations?
Residence, catchment area, common event, occupation;
this is important to determine who is at risk
What are the 4 basic measures of epidemiology?
1) counts
2) ratios
3) proportions
4) rates
Counts: numerator/denominator
of affected individuals in a population/population at risk
Describe ratios.
A/B
**Ratios are used to compare the magnitude of two or more measures
Describe proportions.
(A/A+B)
- *Tells what fraction of the population is affected.
- *Ranges from 0-1 (because it’s a percentage)
- *Has no element of time
Describe rates.
(A/A+B) per 1,000, 10,000, or 100,000
**Rate is a proportion that includes a measure of time in the denominator
Birth rate equation:
live births in a population for one calendar year/population at midyear
Crude death rate equation:
of deaths in a population in a year/population at midyear
Age-specific death rate equation:
for example: # deaths age 15-19 in a year/population age 15-19 at midyear
Age-sex-specific death rate equation:
for example: # of deaths among 5 year old boys in a year/population of 5yo boys at midyear
What is case fatality rate?
It’s a measure of prognosis or the rate at which people die of disease.
What is survival rate?
It’s a measure of prognosis that measures the probability of surviving a specified time period.
We want survival rate to be 100%
What is YPLL?
YPLL: years of potential life lost; measures the relative impact of premature death on society; endpoints may vary and represent that age not considered premature death
Define prevalence.
The number of cases of a given disease that exists in a defined population at a specific time.
Example: ALL cases of lung cancer that exist in Florida in 2012
**most commonly used in cross-sectional studies
What is prevalence rate?
The proportion of a defined population that has a specific disease or attribute at a specified time.
What’s seroprevalence?
The number of persons in a population who test positive for a specific disease based on blood sample specimens.
What are the 3 kinds of prevalence?
1) point prevalence
2) period prevalence
3) lifetime prevalence
Describe point prevalence.
It’s a”snapshot”
of existing cases of a disease at a point in time/total population
**May be a date; i.e. Thanksgiving
Describe period prevalence.
It’s over a period of time… a prevalence RATE
all cases at the beginning of the time and new cases occurring during the time period/everyone in population
What is lifetime prevalence rate?
The proportion of individuals in a population who have had a given disease at any time in their life.
- *used in terms of developing diseases
- *example: breast cancer; car accidents
Define incidence.
The number of new cases or events occurring in a defined population during a specified time period.
**NEW cases in a population
Incidence rate is..
the rate at which new cases occur in a defined population
new cases/population at risk
**measures the risk or probability of an event
What are the two kinds of incidence?
1) Cumulative incidence
2) Incidence density
What is cumulative incidence?
Refers to how frequently new cases of the condition develop in previously disease-free individuals over a period of time
of new cases of disease/total population at risk
- *measures the probability that an individual will develop a disease during a specified period of time
- *EXCLUDE prevalent cases
Does cumulative incidence require complete follow up?
Yes! No one should leave the study and everyone begins at the same time
Describe incidence density.
of new cases of a disease during given time period/total person-time of observation
**denominator is the sum of individual person time at risk/under observation and may be expressed as person-months, person-years, etc.
Why do we need person time?
Person-time accumulates when we observe a group of individuals over a period of time in order to ascertain the DEVELOPMENT of an event.
**people will usually spend different amounts of time in a study
What is the relationship between incidence and prevalence?
Prevalence rate = Incidence Rate x Duration of Disease
1) incidence rate must be constant over time
2) duration of disease must be constant over time
3) the prevalence of disease must be relatively low
What do we mean by “crude” rates?
It’s the entire population; derived by dividing
total # of cases/deaths by total population
Specific rates are…
categories of the population defined by specific characteristic by age, sex, etc. # of cases/deaths in a category by total population in category
What is the main difficulty with crude rates?
There are difficult to compare between groups since underlying characteristic may vary.
**We adjust for differences = standardization
Which characteristic is most routinely adjusted?
AGE! It affects everyone; it’s associated with disease and death
Name two adjustment techniques.
1) Direct adjustment
2) Indirect adjustment
Describe direct adjusted rates.
They are derived by applying the category specific rates of each population to a single standard population;
describes what would have been expected if populations had been identical
adjusted rates are hypothetical
