Measuring Health and Disease

Question 1

List four factors which require accurate measurement of disease occurrence and outcomes to be fully understood.

Answer 1

Impact on the population

Identifying risk factors

Informing public health interventions

Evaluating effectiveness of healthcare programs

Question 2

What elements constitute a ‘clear case definition’?

Answer 2

Standardised criteria that helps to identify individuals/groups/population affected by the health problem/phenomena under study

Who (age, race, gender)

When (seasonal patterns, trends over time)

Where (clusters and spread)

Question 3

Name four sources of health information.

Answer 3

Surveillance systems

Laboratory data

Health records

International organisations

Question 4

List four factors which affect levels of disease occurrence.

Answer 4

Social and behavioural (lifestyle, access to healthcare)

Occupational (work-related risks)

Age and gender

Racial and ethnic

Question 5

Define epidemiological ‘measures’.

Answer 5

Measures are used to relate the number of cases of disease (numerator), or health outcome to the size of the source population (denominator) in which they occurred

Question 6

What variable is the numerator?

Answer 6

Number of cases of disease

Question 7

What variable is the denominator?

Answer 7

Size of the source population

Question 8

True or false: only one of the numerator and denominator variables needs to be defined.

Answer 8

False

Question 9

Describe epidemiological counts.

Answer 9

Also referred to as ‘frequencies’

Used for extremely rare conditions

Count is merely a number

Data is retrieved from surveillance data

Not useful when comparing populations, as the denominators are different

Question 10

Describe epidemiological ratios.

Answer 10

Relationship between two numbers

Usually expressed as x/y x 10n , e.g., number of stillbirths per thousand live births

Numerator is not part of the denominator

Question 11

Discuss epidemiological proportions.

Answer 11

Fraction of a population, or a comparison of a part to the whole

A ratio in which the numerator (x) is included in the denominator (y)

Usually expressed as x/y x 10n, e.g., the number of foetal deaths out of the total number of births

Answer is often read as a percentage

Question 12

Describe epidemiological rates.

Answer 12

How frequently an event happens in a specific population over a certain time frame, e.g., the number of new cases of Parkinson’s disease which develops per 1000 person-years of follow-up

Time, place and population must be specified for each type of rate

In a rate, numerator is not a subset of the denominator
Examples include birth rate, growth rate, accident rate

Frequency across different groups of people, places and time periods

Question 13

List three different types of rates.

Answer 13

Crude rates

Category-specific rates

Age-adjusted rates

Question 14

Both rates and ____________ are often used in public health to quantify mortality and morbidity.

Answer 14

Proportions

Question 15

What is incidence?

Answer 15

The measurement of new cases

Question 16

State six features of incidence.

Answer 16

Considered a rate

Time is essential

It provides information about the risk of developing the disease

Calculated for a given time period

Usually expressed as per 1000 or 100,000 people

Reflects risk of disease or condition

Question 17

What term is synonymous with incidence rate?

Answer 17

Cumulative incidence

Question 18

List features of cumulative incidence.

Answer 18

Measures the denominator only at the beginning of a study

Applies to dynamic populations (e.g., some people are born, die, or move in or out of a region)

Looks at each person in a population, and determines how long they are at risk
Numerator remains the same, denominator is now the sum of person-time (expressed in months or years) at risk

Question 19

Name two other incidence quantifications.

Answer 19

Attack rate

Years of observation (incidence density)

Question 20

What is prevalence?

Answer 20

The measurement of existing illness

Question 21

List six points regarding prevalence.

Answer 21

Prevalence measures the total number of cases (both new and existing) of a disease in a population at a specific point in time

It provides insight into the overall burden of the disease

Considered a proportion

All subjects who appears in the numerator must also appear in the denominator

Point prevalence refers to a particular instance in time

Period prevalence accounts for a particular interval of time (existing cases, together with new cases)

Question 22

List six features which increase prevalence.

Answer 22

Longer duration of the disease

Lifespan increased with treatment

If incidence increases

Immigration of new cases

Improved reporting

Emigration of healthy individuals

Question 23

What are mortality indicators?

Answer 23

Measures of the frequency of occurrence of death in a defined population during a specified period of time

Question 24

Mortality indicators, in the context of a ________ _____, do not take into account that the chance of dying varies with age, sex, race, etc..

Answer 24

Crude rate

Question 25

True or false: mortality indicators are age-specific, but not necessarily cause-specific.

Answer 25

False

Question 26

What are case fatalities?

Answer 26

Proportion of cases with a specified disease or condition, who die within a specified time, and a measure of disease severity

Question 27

A _________ p-value means that observed differences were very unlikely to have occurred by chance, e.g., a p-value of 0.05 indicates that there was only a 5% chance that the observed differences between the two estimates under comparison occurred by chance alone.

Answer 27

Small