Lecture 3

Question 1

What measures do we use to track a population’s health?

Answer 1

Risk factors: Prevalence
Morbidity: disease incidence, disease prevalence, medical care usage
Mortality: total and cause-specific

Question 2

What are the sources of morbidity data?

Answer 2

Health data systems
disease registries 
surveillance systems 
medication/device sales
surveys 
research studies

Question 3

Proportion

Answer 3

Division of two numbers where the numerator is a subset of denominator

Question 4

Rate

Answer 4

A proportion where time is always in deominator

Question 5

How do you measure burden of disease?

Answer 5

Proportions - Number affected / total population

Question 6

How do you measure risk of disease?

Answer 6

Rates - events / population-time

Question 7

Incidence

Answer 7

number of new disease events

Question 8

Incidence rate

Answer 8

rate at which new diseases are occurring

Question 9

Cumulative incidence

Answer 9

cumulative risk for developing new disease among persons over some period of time

Question 10

Incidence rate per 1000

Answer 10

Number of new cases of a disease occurring in the population during a specified interval of time / number of persons at risk of developing the disease during that interval of time X 1000

Question 11

Person-years

Answer 11

(# of subjects) x (years of follow-up per subject)

Question 12

Prevalence per 1000

Answer 12

Number of cases of disease present in the population at a specified time / Number of persons in the population at that specified time X 1000

Question 13

What are the types of prevalence?

Answer 13

Point prevalence

Period prevalence

Question 14

Cumulative incidence (proportion)

Answer 14

Number of new cases of a disease occurring in a population during a specified period of time / Number of person at risk for the disease during that period of time

Question 15

What are estimates of risk?

Answer 15

Incidence rate and Cumulative incidence

Question 16

When is cumulative incidence used commonly?

Answer 16

Period of time = lifetime

Question 17

Prevalence = Incidence x Duration

Answer 17

Higher incidence results in higher prevalence

Longer duration results in higher prevalence

Question 18

What decreases prevalence?

Answer 18

Deaths

Cures

Question 19

Incidence and prevalence for pancreatic cancer

Answer 19

Incidence low
Duration short
Prevalence low

Question 20

Incidence and prevalence for common cold

Answer 20

Incidence high
Duration short
Prevalence low

Question 21

Incidence and prevalence for chronic lung disease

Answer 21

Incidence low
Duration long
Prevalence high

Question 22

Incidence and prevalence for hypertension

Answer 22

Incidence high
Duration long
Prevalence high

Question 23

Factors that increase observed prevalence

Answer 23

Increase in new cases
Longer duration of the disease
Prolongation of life of patient withoutcure
Improved diagnostic facilities (better reporting)
In-migration of cases
Out-migration of healthy people

Question 24

Factors that decrease observed prevalence

Answer 24

Decrease in new cases
Shorter duration of disease
High case-fatality from disease
Improved proportion cases cured
In-migration of healthy people
Out-migration of cases

Question 25

What are the problems with numerators and denominators

Answer 25

Strict criteria to define both Numerator must come from denominator All in the denominator must be able to go into the numerator

Question 26

What are the variability in defining disease?

Answer 26

``` Level of illness (sick, disabled, etc) Specific illness (diagnosis) ```

Question 27

What are the variability in methods of ascertainment?

Answer 27

Using regularly available data (disease reporting, review of medical records) Using specially planned data collection (interviews, direct examinations)

Question 28

What are the issues related to identifying cases?

Answer 28

Variability in defining disease | Variability in methods of ascertainment

Question 29

How could we measure the prevalence of childhood asthma?

Answer 29

questionnaire, physiological measures, medical records

Question 30

"Do you currently have asthma?"

Answer 30

Example of point prevalence

Question 31

"Have you had asthma during the n years?"

Answer 31

Example of period prevalence

Question 32

"Have you ever had asthma?"

Answer 32

Example of cumulative or life-time incidence

Question 33

Limitations of Surveys: Characterizing disease by asking questions

Answer 33

- widely used to describe population health - depend on access to care - depend on recall - subject to bias (limited recall, lack of knowledge, interviewer/informant)

Question 34

Errors in classifying numerators

Answer 34

- bias and variation in self-reporting - variation in disease classification - errors in administrative data bases/medical records (coding for billing purposes, temporal changes, incomplete information, legibility)

Question 35

Problems with denominator

Answer 35

- characterizing the population | - defining the population at risk

Question 36

Major uses of cumulative incidence

Answer 36

Research on causes, prevention, and treatment of disease

Question 37

Major uses of incidence rate

Answer 37

Research on causes, prevention, and treatment of disease

Question 38

Major uses of prevalence

Answer 38

Resource planning