Module 6

Question 1

Definition of variable

Answer 1

Any attribute that describes a person, place, phenomenon, event or idea. Varies in value.

Question 2

What are examples of a variable?

Answer 2

Age
Height
Weight
Income
Education
Sex
Race
Dz status
Diet
Anything that can be studied.

Question 3

Definition of exposure

Answer 3

An independent variable that might cause or prevent a dz or death, a possible determinant.

Question 4

Definition of risk factor

Answer 4

Any exposure that increases a person’s chance of developing a dz or dying.

Question 5

Definition of protective factor

Answer 5

Any exposure that decreases a person’s chance of developing dz or of dying

Question 6

Definition of outcome

Answer 6

A dependent variable that is the effect or consequence of the risk and/or protective factor(s). In epi, this is usually the dz of interest or death.

Question 7

Nominal variable

Answer 7

A type of variable that consists of unordered categories or classes.

Question 8

Examples of nominal variables

Answer 8

Sex
Race/ethnicity,
Sexual orientation
Marital status
Any variable that can have a yes or no value

Question 9

Ordinal variable

Answer 9

Variables with ordered categories but with no consistent distance between them

Question 10

Examples of ordinal variables

Answer 10

Stages of cancer
Levels of education
Values on a Liekert scale (excellent, good, fair poor)

Question 11

Discrete variables

Answer 11

Integers that differ by fixed amounts, with no intermediate values possible

Question 12

Examples of discrete variables

Answer 12

Number of children a parent has
Number of times tails comes up when a coin is flipped

Question 13

Continuous variables

Answer 13

Measurable quantities, not restricted to integer values, with an infinite number of intermediate values. These variables can take on any values between their minimum and maximum values.

Question 14

Examples of continuous variables

Answer 14

Time
Height
Weight
Cholesterol
BP level

Question 15

Study design definition

Answer 15

The set of methods and procedures used by the researchers in collecting and analyzing data to test or generate hypotheses.

Question 16

What are the two major types of study designs in epi?

Answer 16

Experimental
Observational

Question 17

Components of observational studies

Answer 17

Investigator does not have control over the exposure factor
Investigator is unable to assign participants randomly to study conditions
Investigator simply “observes” and lets nature take it course

Question 18

Components of experimental studies

Answer 18

Investigator controls who is exposed to a factor of interest and how much they are exposed to
Investigator assigns participants randomly to study groups
Investigator intervenes

Question 19

What can ecologic studies also go by?

Answer 19

Aggregate and correlate studies

Question 20

Is an ecologic study an observational or experimental study?

Answer 20

Observational

Question 21

What is the unit of analysis in an ecologic study?

Answer 21

Group. This means we compare averages or rates among a sample of groups or units of aggregated data

Question 22

What correlations are obtained in ecologic studies?

Answer 22

Between exposure rates and dz rates among different groups or populations

Question 23

Definition of unit of observation

Answer 23

The level on which data are collected. It is the type of unit you are gathering data about. It is the smallest unit on which the investigators have data.

Question 24

Unit of analysis definition

Answer 24

The level on which data are analyzed and conclusions made.

Question 25

Examples of units of analysis that are groups

Answer 25

A country A state A county A city A neighborhood A school

Question 26

Components of a descriptive ecologic study

Answer 26

May have only an outcome or an exposure variable, but not both. Looks for patterns in the distribution of averages or rates Person, place, or time with no other exposure. No "a priori" hypothesis

Question 27

Components of an analytic ecologic study

Answer 27

Has an outcome and an exposure variable Tests an a priori hypothesis that a specific exposure helps to cause or prevent a specific dz

Question 28

What are the three main types of ecologic studies?

Answer 28

Ecologic comparison study aka multigroup study Ecologic trend study aka time trend Mixed ecologic study

Question 29

What does an ecologic comparison/multi-group study do?

Answer 29

Examines exposure rates and dz rates among different groups over the same time period

Question 30

What does a time trend study/ecologic trend study do?

Answer 30

Examines changes in exposure and changes in dz within the same community, country, or geographic area over time. Units that are compared are time periods.

Question 31

What does a mixed ecologic study do?

Answer 31

Combines aspects of both the ecologic comparison and ecologic trend studies Observes the relationship between the average change in dz incidence in several groups over time

Question 32

Examples of analysis techniques in ecological studies

Answer 32

Usually continuous data Scatter plots Correlation coefficients Linear regression

Question 33

Which axis is associated with what component of the study?

Answer 33

X is exposure and Y is outcome

Question 34

Definition of correlation

Answer 34

A measure of linear association between two ordered lists, or two continuous variables

Question 35

Definition of correlation coefficient

Answer 35

A measure of how nearly a scatter plot falls on a straight line. Always between -1 and 1.

Question 36

When is a correlation positive?

Answer 36

When the coefficient is from 0 to +1. When the coefficient is exactly +1, this is a perfect positive; as one variable goes up, so does the other. The closer it gets to 0, the weaker it is. The closer it gets to +1, the stronger the positive association is.

Question 37

What does a correlation coefficient of 0 indicate?

Answer 37

No association or relationship between the two variables

Question 38

When is a correlation negative or inverse?

Answer 38

When the coefficient is from 0 to -1. A correlation coefficient of -1 is a perfect negative: as one variable goes up, the other comes down. The closer it is to 0, the weaker it is. The closer it is to -1, the stronger the inverse it is.

Question 39

Advantage of ecologic studies

Answer 39

Quick Inexpensive Utilize data that is already available Good approach for generating hypotheses when a dz is of unknown etiology Useful whenever it is desirable to make inferences about the group, and not the individual, such as in evaluating a population intervention or a policy More appropriate than observational studies of individuals when intra-group (within the group) variability is small but inter-group variability is large.

Question 40

For which exposures are ecologic studies best?

Answer 40

Social and environmental exposures

Question 41

What are disadvantages of ecologic studies?

Answer 41

Imprecise measurement of exposure and outcome Difficult to adjust for other factors in the study Ecologic fallacy

Question 42

Ecologic fallacy definition

Answer 42

When incorrect inferences about the individual are made from group level data.