Biostats_2_Incidence, Prevalence, Rates

Question 1

What does incidence measure?

Answer 1

New cases that develop in a population over a certain period of time

Question 2

Why is it important to define the period of time for measuring incidence?

Answer 2

To accurately count the number of new cases

(e.g., weekly incidence vs annual incidence)

Question 3

Does incidence take into account existing cases in the population?

Answer 3

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.

Question 4

What should be included in the denominator when calculating incidence?

Answer 4

Only the population at risk of acquiring the disease

Question 5

What is the attack rate?

Answer 5

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.

Question 6

How is the prevalence of a disease determined?

Answer 6

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.

Question 7

At what point does

Incidencerate × averagedurationofdisease

equal prevalance?

Answer 7

when the prevalance is low

Question 8

What happens to prevalence if survival time increases?

Answer 8

Prevalence increases because patients live longer with the disease.

Question 9

Diseases with short duration (e.g., acute infections like influenza) will have high or low prevalence of disease?

Answer 9

Diseases with short duration (e.g., acute infections like influenza) tend to have lower prevalence despite possibly high incidence rates.

Question 10

How are incidence and prevalence impacted with therapies that lead to faster recovery periods?

Answer 10

Prevalence decreases because effective treatment leads to faster recovery or disease resolution. This however, will have no bearing on the incidence.

Question 11

How are incidence and prevalence impacted with chronic diseases like HIV/AIDS, with the advent of antiretroviral therapy (ART)?

Answer 11

The prevalence increases due to accumulation of cases over time.

Incidence remains unaffected as it measures only new cases.

Question 12

What does stable incidence despite increasing prevalence indicate related to quality of care?

Answer 12

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.

Question 13

What happens to prevalence when new effective treatments are started that improve the recovery time of a disease?

Answer 13

Prevalence decreases because effective treatment leads to faster recovery or disease resolution. This however, will have no bearing on the incidence.

Question 14

What is the effect of improved diagnostic accuracy on chronic disease incidence and prevalence?

Answer 14

It leads to increased incidence and prevalence

More cases are identified as a result of better diagnostics.

Question 15

What happens to incidence and prevalence when diagnostic sensitivity increases?

Answer 15

Incidence increases because more cases are identified, and prevalence increases as more individuals are recognized as having the disease.

Question 16

What role does primary prevention play in disease incidence?

Answer 16

Primary prevention decreases incidence of the disease

An example is hepatitis B vaccination, which decreases incidence of hepatitis D.

Question 17

What happens to incidence and prevalence with extensive vaccine administration?

Answer 17

Incidence decreases as fewer new cases occur

Prevalence also decreases over time.

Question 18

What happens to incidence and prevalence when risk factors decrease?

Answer 18

Incidence decreases as fewer individuals are exposed.

There is a reduction in prevalence over time.

Question 19

What happens to incidence and prevalence when contact between infected and noninfected patients is reduced?

Answer 19

Incidence decreases as transmission is reduced, and prevalence decreases as fewer individuals become infected.

Question 20

When is prevalence greater than incidence?

Answer 20

Prevalence > incidence for chronic diseases, due to
large # of existing cases (eg, diabetes).

Question 21

When does:

Prevalence ≈ incidence

Answer 21

This could occur for short duration diseases
(eg, common cold).

Question 22

When is prevalence significantly less than incidence?

Answer 22

Prevalence < incidence for short duration diseases like the common cold or influenza infections. This can also occur when the mortality is high for diseases.

Question 23

What is the crude mortality rate?

Answer 23

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.

Question 24

How is the cause-specific mortality rate calculated?

Answer 24

By dividing the number of deaths from a particular disease by the total population size

This measure helps assess the impact of specific diseases.

Question 25

What does the case-fatality rate indicate?

Answer 25

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.

Question 26

What happens to prevalence if the mortality rate increases?

Answer 26

Prevalence decreases as more individuals die and are removed from the population. This does not impact the incidence.

Question 27

What is the relationship between prevalence and pretest probability?

Answer 27

Prevalence ∼ pretest probability.

Question 28

How does prevalence impact predictive values?

Answer 28

High prevalence:
High PPV
Low NPV

Question 29

What does a standardized mortality ratio (SMR) of 2.0 indicate?

Answer 29

The observed mortality in a particular group is twice as high as that in the general population

SMR is sometimes used in occupational epidemiology.

Question 30

How is the maternal mortality rate calculated?

Answer 30

By dividing the number of maternal deaths by the number of live births

This measure helps assess the safety of childbirth.

Question 31

What is the crude birth rate?

Answer 31

Defined as the number of live births divided by the total population size

It provides insights into population growth.

Question 32

What rate is calculated by dividing the number of deaths by the total population size?

Answer 32

the crude mortality rate

It provides a general indication of the mortality level in a population.

Question 33

How is the cause-specific mortality rate calculated?

Answer 33

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.

Question 34

What does the case-fatality rate represent?

Answer 34

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.

Question 35

What is the standardized mortality ratio (SMR)?

Answer 35

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.

Question 36

How is the maternal mortality rate calculated?

Answer 36

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.

Question 37

What is defined as the crude birth rate?

Answer 37

Defined as the number of live births divided by the total population size

It provides insight into population growth.