week 2 readings Flashcards
for a common disease, such as the common cold, incidence is reported as
a. percent
b. per 100
c. per 1000
d. per 10000
a
The critical element in defining incidence rate is
___ cases of disease
new
Incidence rate is a measure of ???
Incidence rate is a measure of
events—the disease is identified in a person who
develops the disease and did not have the disease
previously
it is also a measure of risk
is incidence or prevalence a measure of risk (NOT BOTH)
incidence
state the condition for incidence rate to be meaningful regarding the numerator and denominator
For an incidence rate to be meaningful, any
individual who is included in the denominator must
have the potential to become part of the group that is
counted in the numerator
when we wish to calculate incidence, explain how do we identify all new cases in a population during a specified time period?
In certain situations, it may be possible to monitor an entire population over time with tests that can detect newly developed cases of a disease. However, often this is not possible and instead a population is identified and screened for the disease at baseline.
Those who do not have the disease at baseline are followed for the specified time, such as 1 year. They are then rescreened to see if they have developed the disease of interest
define an attack rate
the number of people exposed to a suspect vector who became ill, divided by the number of people who were exposed to that vector
The attack rate does not explicitly specify the time
interval because for many fast acting disease outbreaks
we know that most cases occur within a few hours or
a few days after the exposure and the cases developed months after are considered apart of a novel outbreak
TECHNICALLY IT’S A PROPORTION BUT IT’S JUST CALLED RATE
define prevalence
the number of affected persons
present in the population at a specific time divided by
the number of persons in the population at that time;
that is, what proportion of the population is affected
by the disease at that time?
describe the difference between incidence and prevalence
Prevalence can be viewed as a snapshot or a slice through the population at a point in time at which we
determine who has the disease and who does not. But
in so doing, we are not determining when the disease
developed
why do we use incidence and not prevalence to discern risk
If we wish to measure risk, we must use incidence,
because in contrast to prevalence, it includes only new
cases or events and a specified time period during
which those events occurred
define point prevalence
Prevalence of the disease at a certain point in time. this is what we usually refer to when we mean prevalence
define period prevalence
How many people have had the disease at any point during a certain time period? The time period referred to may be arbitrarily selected, such as a month, a single calendar year, or a 5-year period. Some people may have developed the disease during that period, and others may have had the disease before and died or been cured during that period. The important point is that every person represented by the numerator had the disease at some time during the period specified.
since prevalence isn’t used to measure risk, how is it useful?
Prevalence is an important and useful measure of the burden of disease in a community to inform resource allocation by decision-makers. Prevalence is therefore valuable for planning health services. When we use prevalence, we also want to make future projections and anticipate the changes that are likely to take place in the disease burden.
state two issues with the numerator in morbidity measurements
defining who has the disease, which persons should be included in the numerator
state two issues with the denominator in morbidity measurements
selective undercounting of certain groups in the popula-
tion may occur, difficult to ensure everyone in the group represented by the denominator must have the potential to enter the group that is represented by the numerator,
state the relationship between incidence and prevalence
Prevalence Incidence uration of Disease
describe when you would impose restrictions to mortality rate such that it is called a specific rate (eg age-specific mortality rate)
We may not always be interested in a rate for the entire population; perhaps we are interested only in a certain age group, in men or in women, or in one ethnic group. In putting a restriction on age, for example, the same restriction must apply to both the numerator and the denominator, so that every person in the denominator group will be at risk for entering the numerator group.
describe case fatality
what percentage of people who have
a certain disease die within a certain time after their
disease was diagnosed
why is it difficult to standardize date of onset
we would like to use
the date of disease onset as the beginning of the time
period specified in the numerator. However, date of
disease onset is often hard to standardize since many
diseases develop insidiously (without symptoms) over
a long period of time. As a result, in many chronic
diseases, it may be difficult to determine precisely when
the disease process began
explain the difference between mortality and case fatality
In a mortality rate, the denominator represents the entire population at risk of dying from the disease, including both those who have the disease and those who do not have the disease (but who are at risk of developing the disease). In case-fatality, however, the denominator is limited to those who already have the disease. Thus, case-fatality is a measure of the severity of the disease. It can also be used to measure any benefits of a new therapy; as therapy improves, case-fatality would be expected to decline
is years of potential life lost an index or morbidity or mortality
mortality
what is years of potential life lost a measure of
YPLL is a measure of
premature mortality, or early death
what are the 2 conditions for mortality to be a good indication of incidence
first, when the case-fatality rate is high (as in untreated rabies), and second, when the duration of disease (survival) is short.
define underlying cause (of death)
the disease or injury which initiated the train of morbid events leading directly or indirectly to death or the circumstances of the accident or violence which produced the fatal injury
