Lecture 5 Flashcards
Prevalence Rate
Not a word!!
Say Prevalence proportion
Prevalence
of existing cases of a Dz @ a SPECIFIC POINT IN TIME
• proportion of population taken at a given time
- Dz / total sampled
• Cross-section
Incidence
of NEW EVENTS (e.g., new cases of a disease) in a defined population W/IN A SPECIFIC PERIOD
Limitations of Prevelence
- biased picture
* favors chronic cases over acute cases
* prevalence is related to survival - measuring 2 factors at once, does not prove cause/effect
Incidence
• Preferred measure of Dz occurrence concerns the study of risk factor
Incident cases
New cases
Prevalent cases
Existing cases
Key difference in incidence vs prevalence
- Incidence
- numerator = New cases only
- denominator = Population @ risk
- Incidence
2 ways to measure incidence
• Cumulative incidence (Risk / incidence proportion)
- no units
• Incidence Rate (incidence density)
- unit of time
Cumulative incidence
Risk / incidence proportion
- Indication of AVG RISK of developing a dz DURING a particular time period
- ONLY correct if ALL individuals followed up
- no units
- specific TIME INTERVAL
- can cause results to be inaccurate - over time can only stay the same Or go up
= Developed dz during time period / @ risk from beginning
Incidence Rate
Incidence density
- units of time (Units of Animal-time)
- individuals under observation for varying periods of time
- - helpful for dynamic/open populations!
Crude mortality rate
** if individual time at risk is unknown…?
All deaths / population
• 2 commonly used estimations:
1. Population size @ mid-point in time
2. Initial population + End population
Divided by 2
Cause-specific mortality rate
Deaths from Dz X / population
Case fatality rate
Deaths from Dz X / # animals w. Dz X
Proportionate mortality
Ratio of Dz X / all deaths
