Descriptive Epidemiology (ch. 5 and 6)

Question 0

Define denominator.

Answer 0

The population: a group of people with a common characteristic; populations determine who is at risk.

Question 1

WHO’s definition of health:

Answer 1

physical, mental, and social well-being

Question 2

How can we define populations?

Answer 2

Residence, catchment area, common event, occupation;

this is important to determine who is at risk

Question 3

What are the 4 basic measures of epidemiology?

Answer 3

1) counts
2) ratios
3) proportions
4) rates

Question 4

Counts: numerator/denominator

Answer 4

of affected individuals in a population/population at risk

Question 5

Describe ratios.

Answer 5

A/B

**Ratios are used to compare the magnitude of two or more measures

Question 6

Describe proportions.

Answer 6

(A/A+B)

• *Tells what fraction of the population is affected.
• *Ranges from 0-1 (because it’s a percentage)
• *Has no element of time

Question 7

Describe rates.

Answer 7

(A/A+B) per 1,000, 10,000, or 100,000

**Rate is a proportion that includes a measure of time in the denominator

Question 8

Birth rate equation:

Answer 8

live births in a population for one calendar year/population at midyear

Question 9

Crude death rate equation:

Answer 9

of deaths in a population in a year/population at midyear

Question 10

Age-specific death rate equation:

Answer 10

for example:
# deaths age 15-19 in a year/population age 15-19 at midyear

Question 11

Age-sex-specific death rate equation:

Answer 11

for example:
# of deaths among 5 year old boys in a year/population of 5yo boys at midyear

Question 12

What is case fatality rate?

Answer 12

It’s a measure of prognosis or the rate at which people die of disease.

Question 13

What is survival rate?

Answer 13

It’s a measure of prognosis that measures the probability of surviving a specified time period.
We want survival rate to be 100%

Question 14

What is YPLL?

Answer 14

YPLL: years of potential life lost; measures the relative impact of premature death on society; endpoints may vary and represent that age not considered premature death

Question 15

Define prevalence.

Answer 15

The number of cases of a given disease that exists in a defined population at a specific time.
Example: ALL cases of lung cancer that exist in Florida in 2012

**most commonly used in cross-sectional studies

Question 16

What is prevalence rate?

Answer 16

The proportion of a defined population that has a specific disease or attribute at a specified time.

Question 17

What’s seroprevalence?

Answer 17

The number of persons in a population who test positive for a specific disease based on blood sample specimens.

Question 18

What are the 3 kinds of prevalence?

Answer 18

1) point prevalence
2) period prevalence
3) lifetime prevalence

Question 19

Describe point prevalence.

Answer 19

It’s a”snapshot”

of existing cases of a disease at a point in time/total population

**May be a date; i.e. Thanksgiving

Question 20

Describe period prevalence.

Answer 20

It’s over a period of time… a prevalence RATE

all cases at the beginning of the time and new cases occurring during the time period/everyone in population

Question 21

What is lifetime prevalence rate?

Answer 21

The proportion of individuals in a population who have had a given disease at any time in their life.

• *used in terms of developing diseases
• *example: breast cancer; car accidents

Question 22

Define incidence.

Answer 22

The number of new cases or events occurring in a defined population during a specified time period.

**NEW cases in a population

Question 23

Incidence rate is..

Answer 23

the rate at which new cases occur in a defined population

new cases/population at risk

**measures the risk or probability of an event

Question 24

What are the two kinds of incidence?

Answer 24

1) Cumulative incidence

2) Incidence density

Question 25

What is cumulative incidence?

Answer 25

Refers to how frequently new cases of the condition develop in previously disease-free individuals over a period of time

of new cases of disease/total population at risk

• *measures the probability that an individual will develop a disease during a specified period of time
• *EXCLUDE prevalent cases

Question 26

Does cumulative incidence require complete follow up?

Answer 26

Yes! No one should leave the study and everyone begins at the same time

Question 27

Describe incidence density.

Answer 27

of new cases of a disease during given time period/total person-time of observation

**denominator is the sum of individual person time at risk/under observation and may be expressed as person-months, person-years, etc.

Question 28

Why do we need person time?

Answer 28

Person-time accumulates when we observe a group of individuals over a period of time in order to ascertain the DEVELOPMENT of an event.

**people will usually spend different amounts of time in a study

Question 29

What is the relationship between incidence and prevalence?

Answer 29

Prevalence rate = Incidence Rate x Duration of Disease

1) incidence rate must be constant over time
2) duration of disease must be constant over time
3) the prevalence of disease must be relatively low

Question 30

What do we mean by “crude” rates?

Answer 30

It’s the entire population; derived by dividing

total # of cases/deaths by total population

Question 31

Specific rates are…

Answer 31

categories of the population defined by specific characteristic by age, sex, etc. 
# of cases/deaths in a category by total population in category

Question 32

What is the main difficulty with crude rates?

Answer 32

There are difficult to compare between groups since underlying characteristic may vary.

**We adjust for differences = standardization

Question 33

Which characteristic is most routinely adjusted?

Answer 33

AGE! It affects everyone; it’s associated with disease and death

Question 34

Name two adjustment techniques.

Answer 34

1) Direct adjustment

2) Indirect adjustment

Question 35

Describe direct adjusted rates.

Answer 35

They are derived by applying the category specific rates of each population to a single standard population;
describes what would have been expected if populations had been identical

adjusted rates are hypothetical