what are the two components of epidemiology?
- descriptive
- analytic
what are the 5 Ws of epidemiology?
- what
- when
- where
- who
- why/how
what is descriptive epidemiology?
- Describes the DISTRIBUTION of health related stated and
events - Describes the FREQUENCY and PATTERN of health-
related states and events - Describes the WHO, WHERE, and WHEN
- Person (who)
- Place (where)
- Time (when)
- Communicates public health problem with the use of tables and graphs
types of trends in time: secular trends
long-term changes in health-related states or events
e.g. development of liver disease can take years on average from alcohol abuse
types of trends in time: short-term trends
brief, often unexpected increases in health-related states or events
e.g. salmonella outbreak
types of trends in time: cyclic trends
periodic increases and decreases in the occurrences of health-related states or events
e.g. influenza infection during flu season
Measures of Disease Occurrence: counts
- Counts
- Number (n)
- Frequency (f)
- Just one number
- Answers the question of ‘how many?’
Measures of Disease Occurrence: ratios
- Compares two things
- Divide the numerator by the denominator
- Expressed as X/Y or X:Y
- Numerator may or may not be part of the denominator
- The numerator and denominator may or may not be
related
ratio: portion
- Numerator is always a part of the denominator
- Calculated as: p = A
A+B - Usually calculated as a decimal e.g., 1/8 =.125
- May be presented as a fraction e.g., 1/8
ratio: percentages
- Numerator is always a part of the denominator
- Just a proportion multiplied by 100 (1/8 =.125 = 12.5%)
ratio: rates
- Frequency of an event in a population in a specified period of time
- Population is always specified
- Time period is always specified
- A rate is a proportion that it represents the number of health-related states or events in a population over a specified period
- Adjusted rates -> very important concept for calculating proportions and rates accurately
what are the four types of descriptive studies?
- Case reports
- Case series
- Cross-sectional surveys
- Ecologic studies
what does a case report involve?
a profile of a single individual
**provide evidence for larger scale studies (hypothesis generating)
what does case series involve?
a small group of patients with a similar diagnosis
**provide evidence for larger scale studies (hypothesis generating)
what is a cross-sectional survey?
- Conducted over a short period of time (usually a few
days or weeks) and the unit of analysis is the individual - There is no follow-up period
- Also called prevalence survey
what does prevalence mean?
the number of a disease present in a population at a certain time
what are cross-sectional survey strengths?
- Can be conducted over a short period of time
- Produces prevalence data
- Can provide evidence of the need for analytic epidemiologic study
- Can be used to study several associations at once
what are cross-sectional study weaknesses?
- Unable to establish sequence of events
- Infeasible for studying rare conditions
- Potentially influenced by response bias
what are some cross-sectional surveys that are routinely conducted?
- United States Census
- Behavior Risk Factor Surveillance System
- National Health Interview Survey
- National Hospital Discharge Survey
what is ecologic fallacy?
finding from populations may not apply to individuals
what are the marker of health status? (5)(health indicators)
- Physical or mental illness
- Impairments or disabilities
- Social well being
- Service provision
- Resource availability
what are categories of health indicators? (7)
- Health and well-being
- Health resources
- Collective justice
- Social capital
- Collective capacity
- Resiliency
- Functionality
what is the goal of health surveillance?
to “watch over” the nation’s health
what does public health surveillance use data for?
to monitor health problems to facilitate their prevention or control
