Measure Of Disease Occurence Flashcards
Why should you measure disease?
- To identify important diseases and changing disease patterns
- To compare disease in groups to establish what the risk factors are an there causes
What two types of health problems is epidemiology concerned with ?
- The presence of existing health problems in a population
2. The occurrence of new health events in a population (and their measurement)
Epidemiologists measure:
- The amount of disease in population at one point in time, or over a period of time
- The change in the amount of disease in a population over a period of time
When measuring disease occurrence it is important to define:
4 things
- What is being measured
- The persons or animals included in the measurement (study population)
- Place or location of the study population
- Time period of the study
Which is NOT one of the 3 types of populations that measure disease occurrence ?
A. Source population
B. Target population
C. Spanning population
D. Study population
C. Spanning population
Define study population:
- animals you actually measure (subjects in the study)
- usually a ‘sample’ from a source
- the number ‘n’ of subjects in the study population
Define source population:
Population from which the subjects were drawn
Define target population:
Population to which we may want to generalize our results
What are the 4 most common types of measure in epidemiology?
Counts
Proportions
Ratios
Rates
The number of animals that. Have the disease (or condition of interest) is what type of measure ?
Count
Disadvantage: doesn’t tell you how many of the total population had the disease; they convey very little information
The count of animals w/ the disease, as a fraction of the total animals that could be disease is called what?
Proportion
Main measure of disease occurrence
Often expressed as fractions or percentages
The most commonly used proportion in epidemiology is ________
Prevalence
A fraction in which the numerator is not part of the denominator. (Comparing two different things) is called a _______
Ratio
A commonly used ratio in epidemiology is the odds
Rates measure ________ (old/new) events (choose one)
New
Define rate:
A measure of the frequency with which an event occur in a defined population over a specified period of time
The most commonly used rates in epidemiology are:
Cumulative incidence and incidence rate
Prevalence:
The proportion of the study population that is diseases at any one time (point in time or period)
Provides info about how frequently you might expect to see the condition in your practice
- the probability of an animal from the study population being diseased
How do you calculate point prevalence ?
Number of cases of disease present in the population at a particular time / total population at that time
Incidence:
The number of new cases of disease that occur in the study population over time
- the probability of a disease-free animal from the study population becoming diseased (risk of becoming diseased)
Cumulative incidence:
The proportion of disease-free individuals in the study population who became diseased during a specified period of time
Based on assumptions
The entire population at risk must be followed Fromm the start of the study until the end
Attack rate:
A cumulative incidence during an outbreak
Applied to a narrowly-defined population
Probability of becoming diseased during the course of an outbreak
Incidence rate (2nd kind of incidence):
Instantaneous rate of occurrence of new cases of disease among non-diseased animals in the population
Prevalence vs. incidence
Prevalence: a measure of the amount of disease in a population (includes all cases, old and new) [Used for chronic conditions]]
Incidence: a measure of the rate of disease occurrence. (Only new cases) [Used for acute cases]
Prevalence depends on::
- Incidence and,
2. Duration of disease
