Chapter 14

Question 1

What does a correlational, ecological, or aggregate study do?

Answer 1

Uses population-level data to examine the relationship between exposure rates and disease rates.

Question 2

Correlational studies that explore an environmental exposure may be called:

Answer 2

Ecological studies

Question 3

Why are correlational studies also called aggregate studies?

Answer 3

Because they only look at aggregate, or grouped, population-level data, and they do not include any individual level data.

Question 4

What type of study are correlational studies?

Answer 4

Secondary study

Question 5

What is the key to success for correlational studies?

Answer 5

Identifying data sources that contain comparable information about the variables of interest.

Question 6

What is a requirement of correlational studies?

Answer 6

The topic must not have been previously explored using individual level-data

Question 7

What is the key statistical measure for correlational studies

Answer 7

Correlation

Question 8

Most exposures and outcomes used in correlational studies are in the form of:

Answer 8

Population-level statistics

Question 9

What should be done before conducting a statistical analysis of aggregate data?

Answer 9

The data from each population must be entered into a spreadsheet. Each population should have its own row, and each exposure and outcome should be assigned to its own column.

Question 10

The correlational study analysis will only be valid if:

Answer 10

The data points are comparable.

Question 11

What might interfere with the definition of an exposure or a disease from one population to another in a correlational study?

Answer 11

1) Multiple sources of data are used.

2) The data was collected over a lengthy period of time.

Question 12

On a scatter plot used to illustrate correlation what does each point represent?

Answer 12

One population in the study

Question 13

What is plotted on the x-axis and the y-axis of a scatterplot for a correlational study?

Answer 13

X-axis: Exposure

Y-axis: Outcome/disease

Question 14

When all points fall neatly along or a very near a sloped line, the correlation is _______. A positive (upward) slope shows that _____. A negative (downward) slope shows that ____.

Answer 14

Very strong; higher levels of exposure are associated with higher rates of disease; higher levels of exposure are associated with lower rates of disease.

Question 15

When the points are not exactly linear but a line for trends can be drawn through them, the correlation is ____.

Answer 15

Mild or moderate

Question 16

When the points appear to be randomly placed and no obvious line can be drawn through them, or the best-fit line is horizontal, then the correlation is ____.

Answer 16

Weak or nonexistent

Question 17

When do we use Pearson correlation coefficient (r)?

Answer 17

For continuous variables and other variables with responses that can be plotted on a number line.

Question 18

When do we use Spearman rank-order correlation (rho)?

Answer 18

For variables that assign a rank to responses or that have ordered categories.

Question 19

For both the Pearson and Spearman correlation tests, r=-1 means:

Answer 19

Very strong negative correlation

Question 20

For both the Pearson and Spearman correlation tests, r=0 means:

Answer 20

No association between the exposure and outcome.

Question 21

For both the Pearson and Spearman correlation tests, r=+1 means:

Answer 21

Very strong positive correlation

Question 22

What is the coefficient of determination?

Answer 22

It shows how strong a correlation is without indicating the direction of the association. (0 = no correlation, 1= perfect)

Question 23

If two populations differ in age what should be done?

Answer 23

Age adjustment

Question 24

What does direct age adjustment require?

Answer 24

Knowing the exposure or disease rates by age group in each population

Question 25

When do we use indirect age adjustment?

Answer 25

When comparing populations for which the population age distributions are known, but age-specific rates of exposure and/or disease are not known.

Question 26

What is the ecological fallacy?

Answer 26

The incorrect attribution of population–level associations to individuals.

Question 27

True or false:

An individual from a country with a high average BMI will be obese.

Answer 27

False; this is a population-level trend and it is incorrect to assume that every individual follows the trend.

Question 28

Correlational studies are useful starting point for:

Answer 28

Generating hypotheses about associations, but they are not the final word on risk factors for disease.