Incidence, Prevalence, Rates (Biostats) Flashcards
What does incidence measure?
New cases that develop in a population over a certain period of time
Why is it important to define the period of time for measuring incidence?
To accurately count the number of new cases
(e.g., weekly incidence vs annual incidence)
Does incidence take into account existing cases in the population?
No.
Incidence does not take into account the number of cases that already existed before the counting period.
Incidence only counts for the newly developed cases that during a stated period.
What should be included in the denominator when calculating incidence?
Only the population at risk of acquiring the disease
What is the attack rate?
An incidence measure calculated by dividing the number of patients with disease by the total population at risk
The attack rate is a measure of the frequency of disease occurrence in a specific population during an outbreak or epidemic. It is often used in epidemiology to describe the proportion of people who become ill after exposure to a specific risk or pathogen. The attack rate is essentially a form of incidence rate but is typically used for acute outbreaks over a short period.
If 80 people in a town are exposed and 60 people become ill, attack rate is … ?
75%
How is the prevalence of a disease determined?
Prevalence measures all existing cases (both new and old).
If individuals live longer with the disease due to better treatments or care, more cases accumulate, increasing prevalence.
At what point does …
( Incidencerate × averagedurationofdisease )
… equal prevalance?
when the prevalance is low
What happens to prevalence if survival time increases?
Prevalence increases because patients live longer with the disease.
Diseases with short duration (e.g., acute infections like influenza) will have high or low prevalence of disease?
Diseases with short duration (e.g., acute infections like influenza) tend to have lower prevalence despite possibly high incidence rates.
How are incidence and prevalence impacted with therapies that lead to faster recovery periods?
Prevalence decreases because effective treatment leads to faster recovery or disease resolution. This however, will have no bearing on the incidence.
How are incidence and prevalence impacted with chronic diseases like HIV/AIDS, with the advent of antiretroviral therapy (ART)?
The prevalence increases due to accumulation of cases over time.
Incidence remains unaffected as it measures only new cases.
What does stable incidence despite increasing prevalence indicate related to quality of care?
A stable incidence despite increasing prevalence indicates better management of existing cases. It is usually related to improved quality of care and resultant decrease in mortality.
What happens to prevalence when new effective treatments are started that improve the recovery time of a disease?
Prevalence decreases because effective treatment leads to faster recovery or disease resolution. This however, will have no bearing on the incidence.
What is the effect of improved diagnostic accuracy on chronic disease incidence and prevalence?
It leads to increased incidence and prevalence
More cases are identified as a result of better diagnostics.
What happens to incidence and prevalence when diagnostic sensitivity increases?
Incidence increases because more cases are identified, and prevalence increases as more individuals are recognized as having the disease.
What role does primary prevention play in disease incidence?
Primary prevention decreases incidence of the disease
An example is hepatitis B vaccination, which decreases incidence of hepatitis D.
What happens to incidence and prevalence with extensive vaccine administration?
Incidence decreases as fewer new cases occur
Prevalence also decreases over time.
What happens to incidence and prevalence when risk factors decrease?
Incidence decreases as fewer individuals are exposed.
There is a reduction in prevalence over time.
What happens to incidence and prevalence when contact between infected and noninfected patients is reduced?
Incidence decreases as transmission is reduced, and prevalence decreases as fewer individuals become infected.
What occurs with prevalence and incidence with chronic illnesses?
Prevalence surpasses incidence for chronic diseases, due to large # of existing cases (eg, diabetes) over the new occurrence rate.
When does:
Prevalence ≈ incidence
This could occur for short duration diseases
(eg, common cold).
When is prevalence significantly less than incidence?
Prevalence < incidence for short duration diseases like the common cold or influenza infections. This can also occur when the mortality is high for diseases.
Deaths/1000 people per year is the calculation for … ?
Mortality rate (number of deaths (in general or due to specific cause) within a population over a defined period.
If 80 people in a town of 10,000 die over 2 years, mortality rate is …. ?
4 per 1000 per year
What is the crude mortality rate?
Calculated by dividing the total number of deaths by the total population size then multiplying by 100,000 to get a value for the number of deaths per 100,000 in the population.
It provides a general measure of mortality An indication of the health status in a population.
How is the cause-specific mortality rate calculated?
By dividing the number of deaths from a particular disease by the total population size
This measure helps assess the impact of specific diseases.
What does the case-fatality rate indicate?
Calculated by dividing the number of deaths from a specific disease by the number of people affected by the disease
It reflects the severity of the disease.
If 4 patients die among 10 cases of meningitis, case fatality rate is … ?
40%
What happens to prevalence if the mortality rate increases?
Prevalence decreases as more individuals die and are removed from the population. This does not impact the incidence.
What is the relationship between prevalence and pretest probability?
Prevalence ≈ pretest probability.
How does prevalence impact predictive values?
High prevalence:
High PPV
Low NPV
What does a standardized mortality ratio (SMR) of 2.0 indicate?
The observed mortality in a particular group is twice as high as that in the general population
SMR is sometimes used in occupational epidemiology.
How is the maternal mortality rate calculated?
By dividing the number of maternal deaths by the number of live births
This measure helps assess the safety of childbirth.
What is the crude birth rate?
Defined as the number of live births divided by the total population size
It provides insights into population growth.
What rate is calculated by dividing the number of deaths by the total population size?
the crude mortality rate
It provides a general indication of the mortality level in a population.
How is the cause-specific mortality rate calculated?
Calculated by dividing the number of deaths from a particular disease by the total population size
This rate helps in understanding the impact of specific diseases on the population.
What does the case-fatality rate represent?
Calculated by dividing the number of deaths from a specific disease by the number of people affected by the disease
It indicates the severity of a disease and the effectiveness of treatment.
What is the standardized mortality ratio (SMR)?
Calculated by dividing the observed number of deaths by the expected number of deaths
An SMR of 2.0 indicates that the observed mortality is twice as high as that in the general population.
How is the maternal mortality rate calculated?
Calculated by dividing the number of maternal deaths by the number of live births
It is a crucial indicator of maternal health and healthcare quality.
What is defined as the crude birth rate?
Defined as the number of live births divided by the total population size
It provides insight into population growth.
