Descriptive Epidemiology

Question 2

What is the definition of epidemiology?

Answer 2

Epidemiology is defined as the study of the distribution and determinants of disease frequency in human populations and the application of this study to control health problems.

This definition emphasizes both the study aspect and the practical application in public health.

Question 3

What does descriptive epidemiology focus on?

Answer 3

Descriptive epidemiology focuses on describing the distribution of disease and analyzing disease patterns according to characteristics of person, place, and time.

These characteristics help in understanding how diseases affect different populations.

Question 4

What are the characteristics analyzed in descriptive epidemiology?

Answer 4

Descriptive epidemiology analyzes disease patterns according to:
* Person
* Place
* Time

These characteristics help identify trends and variations in disease occurrence.

Question 5

What is the purpose of using descriptions in descriptive epidemiology?

Answer 5

Descriptive epidemiology is used to assess the health of a population, generate hypotheses about causal factors, and plan and evaluate public health programs.

This process helps in identifying health issues and potential interventions.

Question 6

What are the three time-related variables that can influence health outcomes?

Answer 6

Biologic age, calendar time, year of birth

These variables can affect the risk and rate of health outcomes simultaneously.

Question 7

Fill in the blank: _______ can influence the risk/rate of health outcomes.

Answer 7

Age, Period and Cohort Effects

Question 8

True or False: Age, Period, and Cohort Effects only influence health outcomes one at a time.

Answer 8

False

They can influence health outcomes simultaneously.

Question 9

Define and provide an example of age effects

Answer 9

Variation in health status that arises from aging

Question 10

Define and provide an example of period effects

Answer 10

Variation in health status that arises from changes in the environment during a given period of time

Often happens to the whole group (pandemic, war, recession)

Question 11

Define and provide an example of cohort effects

Answer 11

Variation in health status that arises from the different causal factors (e.g., infectious agents) to which each birth cohort is exposed as the environment and society change.

*happens in cohorts and may vary from group to group

Question 12

What is a population?

Answer 12

A group of people with a common characteristic such as place of residence, age or the occurrence of an event.

Question 13

Total population

Answer 13

Includes everyone in the population – sick, healthy, at risk, and not at risk.

All residents of the U.S.

Question 14

Fixed/closed population

Answer 14

Membership is defined by a fixed event.
In the context of a study, a closed study enrolls participants over a set time period and then no further participants are enrolled (although some may leave).

Residents of NYC on 9/11/2001

Question 15

Open populations (1)
1) Dynamic

Answer 15

Membership is based on a state that is transitory. In the context of a study, an open study continues to enroll participants over the course of the study

Residents of a city, patients in a particular hospital

Question 16

Open populations (2)
2) Steady state OR dynamically stable

Answer 16

Number of people entering/being born is roughly equal to the number of people exiting/dying. Refers to the total population AND the distribution of other factors (covariates) that might affect exposure and disease frequency in the population.

UC Berkeley student population from year to year

Question 17

What are the three measures of disease frequency?

Answer 17

Ratios, proportions, and rates

These measures help in understanding the relationship between different quantities in epidemiology.

Question 18

What is the formula used for ratios, proportions, and rates?

Answer 18

a / b

‘a’ and ‘b’ represent the two quantities being compared.

Question 19

In a ratio, how are the values of a and b related?

Answer 19

They may be completely independent, or a may be included in b

For example, comparing the number of females to males or female to all

Question 20

What characterizes a proportion?

Answer 20

The value of a is included in b.

women/all

Proportions are a specific type of ratio.

Question 21

What is a rate in the context of disease frequency measures?

Answer 21

A type of proportion with time as an integral part of the denominator

Rates measure the occurrence of disease over a specified time period.

Question 22

What is the formula for calculating a rate?

Answer 22

Rate = Number of new cases or deaths occurring during a given time period / Total person-time at risk

This formula helps assess the disease status relative to the population size.

Question 23

What must the person-time in the denominator represent?

Answer 23

It must be at risk for the event

This ensures that the individuals counted had the possibility to experience the event.

Question 24

True or False: A rate can measure the disease status of a population without considering time.

Answer 24

False

Time is a crucial component of the rate calculation.

Question 25

Incidence Density (ID), Incidence Rate (IR) (rate)

Answer 25

numerator: # of new cases of a specified disease reported during a given time interval denominator: Total person-time contributed by individuals at risk during a given time interval | expressed as cases, events or deaths per person-time ## Footnote Range = 0 to ∞ Units: 1/time

Question 26

Cumulative Incidence (CI), Risk (proportion)

Answer 26

numerator: # of new cases of a specified disease reported during a given time interval denominator: Total population at risk at the beginning of the time interval | expressed as cases, events or deaths per number of people at risk ## Footnote Range = 0 to 1 Units: No units

Question 27

Prevalence (point or period) (proportion)

Answer 27

numerator: # of existing cases of a specified disease at a given point or period in time denominator: Estimated number in total population at the same point in time | expressed as cases, events or deaths per population ## Footnote Range = 0 to ∞ Units: No units

Question 28

Odds (odds)

Answer 28

Probability an event will occur (p)/1 minus the probability an event will occur (1-p) or probability the event will not occur | expressed as odds of an event occurring ## Footnote Range = 0 to ∞ Units: No units

Question 29

Incidence density*duration

Answer 29

Prevalence / (1-Prevalence) | Prevalence ≅ Incidence Density * Duration when disease is rare ## Footnote (prevalence <10%)

Question 30

When disease is rare (CI <10%), time period is short, population is fixed and ID is constant over the time period, how do we calculate cumulative incidence?

Answer 30

Incidence Density * Time