MEASURES OF DISEASE FREQUENCY & MORBIDITY (PART 2) Flashcards
State of being symptomatic or unhealthy for a
disease/condition
MORBIDITY
Presence of disease in a population
MORBIDITY
Comorbidity-state of having 2
morbidities
Presence of disease in a population
Two categories of measurement to describe
Morbidity Frequency of disease in a specified
population:
○ Incidence (new cases)
○ Prevalence (existing cases-old &
new)
Occurrence of new cases of events (disease,
injury, death, etc.) in a population at risk over a
specified period of time.
INCIDENCE/INCIDENT CASES
Number of transitions
INCIDENCE/INCIDENT CASES
INCIDENCE/INCIDENT CASES Types:
○ Incidence Proportion/Risk
○ Incidence Rate/Person-Time Rate
The proportion of initially disease-free
the population that develops new cases of the disease in a specified period of time
INCIDENCE PROPORTION/RISK
Measures the probability that healthy people will
develop the disease during a specified time.
INCIDENCE PROPORTION/RISK
INCIDENCE PROPORTION/RISK SYNONYMS
○ Attack Rate
○ Incidence Risk
○ Probability of Developing Disease
○ Cumulative Incidence
INCIDENCE PROPORTION OF
OVARIAN CANCER
■ Numerator- _____________
■ Denominator- ____________
New cases of
ovarian cancer; Number of
women
INCIDENCE PROPORTION/RISK CRITERIA NEEDED
○ Knowledge of health status of the study
population
○ Time of onset (acute vs chronic)
○ Specification of numerator
○ Specification of population “at risk”
○ Period of observation
Denominator shouldn’t
include people who are ____________________
NOT
susceptible
Number of persons at risk
varies over time. If so, consider
using population size at
________ of the time period.
mid-point
PERIOD OF OBSERVATION FOR INCIDENCE PROPORTION/RISK
usually 1 year
attack rate =
= (# of persons who suffered from attack/ total # of persons at risk of attack) 10^N
form of incidence that measures the proportion of persons in a population who experience an acute health event during a limited period
attack rate
total number of new cases divided by total population
overall attack rate
number of persons who ate and became ill divided by total number of persons who ate the food
Food-specific attack rate
spread of disease in a family, household, dwelling unit, dormitory, or similar circumscribed group
Secondary attack rate
Secondary attack rate =
(number of cases among contacts of primary cases/ total number of contacts) x 10^n
total number of contacts =
total population of household minus P^o cases
AKA incidence density
INCIDENCE RATE/PERSON-TIME RATE
Measure of incidence that incorporates time
directly into the denominator.
INCIDENCE RATE/PERSON-TIME RATE
Estimates how quickly people are acquiring the
disease
INCIDENCE RATE/PERSON-TIME RATE
Calculated from long-term cohort follow up
study
INCIDENCE RATE/PERSON-TIME RATE
person-months/ persona years of observation
Person-time
Risk period is short
INCIDENCE PROPORTION
Likely to observe the whole
period
INCIDENCE PROPORTION
Risk period is long
INCIDENCE RATE
Length of study follow
up period will vary
from study to study
INCIDENCE RATE
Ex. food poisoning
INCIDENCE PROPORTION
Ex. most cancers
INCIDENCE RATE
Want to know what proportion
of population became
infected
INCIDENCE PROPORTION
Want to know the rate
at which new
infections occur
INCIDENCE RATE
What is the risk that an
individual will develop the
disease over a given time
interval?
INCIDENCE PROPORTION
How quickly or
frequently does a
disease occur in a
population?
INCIDENCE RATE
Not a measure of risk
PREVALENCE
Proportion of persons in a population when a
particular disease or attribute at a specified point
in time/period
PREVALENCE
Usually expressed as a percentage
. PREVALENCE
Used to express burden of disease (new + old /
pre existing case)
PREVALENCE
Types of prevalence
○ Point prevalence
○ Period Prevalence
Proportion of persons with a particular
disease or attribute on a particular
date.
Point Prevalence
The proportion of persons with a particular
disease or attribute at any time during
the interval.
Period Prevalence
“Do you currently have asthma?”
point of prevalence
“Have you had asthma during the last (n) years?”
Period of prevalence
Proportion/rate of a persons
who develop a condition
during a particular period
INCIDENCE
New and pre-existing
cases (Numerator)
PREVALENCE
Proportion of persons
who have condition
at/during particular
time period
PREVALENCE
New cases only (Numerator)
INCIDENCE
