Chapter 12: Design Tools

Question 1

What is a variable?

Answer 1

• A factor or attribute that can assume two or more values
• Variables can vary
• Variability is wonderful in some cases but not
others – examples?

Question 2

What is a domain?

Answer 2

• Domain is all possible values that a variable can have

* Smallest domain is two (dichotomous or binary)

Question 3

What is a qualitative variable? Give examples

Answer 3

• properties that vary in a type of attribute

* Examples: sex, religion, eye color, marital status

Question 4

What is a quantitative variable? Give examples

Answer 4

• Properties that different in an amount

* Examples: height, weight, blood pressure

Question 5

What is a discrete variable?

Answer 5

• Quantitative adjacent variable in which no intermediate
values are possible
• Can we have 1.5 and 2.8 children?

Question 6

What is a continuous variable?

Answer 6

• Intermediate values are possible in between two
adjacent scale values
• Examples: height, weight, blood pressure
• But, in practice these are usually converted into discrete variables

Question 7

What is an independent variable?

Answer 7

• Presumed causal factor in a cause-effect relationship

* In an experiment, this is what you manipulate (X-axis)

Question 8

What is a dependent variable?

Answer 8

• Presumed effect in a cause-effect relationship
• “depends” upon the independent variable
• In an experiment, this is the outcome you measure (Y- axis)

Question 9

What is mediator variable?

Answer 9

• X –> Mediator Variable –> Y
• Variable to explain why the two are linked…provides the CAUSAL link
• Fish Consumption –> ____________ –> IQ (+)
• Fish Consumption –> ____________ –> IQ (-)

Question 10

What is moderating variable?

Answer 10

• (X --> Y) * moderator (M)
• Variable that alters the strength or direction of the
relationship
• Aka interaction terms
• (Fish Consumption --> IQ) * M

Question 11

Mediator variable vs moderating variable

Answer 11

A mediating variable explains the relation between the independent (predictor) and the dependent (criterion) variable. … A moderator is a variable that affects the strength of the relation between the predictor and criterion variable. Moderators specify when a relation will hold.

Question 12

What is confounding variable?

Answer 12

• Variable (C) that correlates with both X and Y
• Not in the causal pathway
• Causes confusion in the true relationship

Question 13

What are conceptual and operational variables?

Answer 13

• Scientists need to be explicit on how they define
their variables
• Conceptual variables are the “ideas”
• Must provide operational definitions AND how to measure these (method? valid?)
• Scientists can disagree on how to define certain variables (IQ? Cardiovascular disease?)
• Disagreements can be frustrating… can lead to poor decisions… may lead to debate and progress

Question 14

What are the 4 scales of measurement?

Answer 14

• nominal
• ordinal
• interval
• ratio

Question 15

Define measurement

Answer 15

A process of systematically assigning values to variables

Question 16

Define nominal scale and give examples

Answer 16

qualitative differences in scale values
• Sex, politics, college major, food categories, menu offerings, computer folders, hair color, birth city
• labels

Question 17

Define ordinal scale and give examples

Answer 17

different scale values represent relative
differences, and the “order” matters
• Rank ice cream preferences; Likert scales (how do you feel today? My teaching score?); Apgar score

Question 18

Define interval scale and give examples

Answer 18

Scale values have equal and exact distance

• Temperature, time of day, calendar year

Question 19

Define ratio scales and give examples

Answer 19

Interval BUT has an absolute zero
• Is 20’C 2x hotter than 10’C? Is 10pm 5x later than 2pm?
• Time, length, annual income, caloric intake, pregnancies, money, etc
• True ratios can be calculated

Question 20

What is accuracy (validity)?

Answer 20

• The degree to which the measurement yields results that agree with the truth
• 5 systolic blood pressure readings yield 138, 140, 143, and 144 mmHg (mean = 141.25)
• True measure is 131
• Systemic error (bias) in the instrument?
• Ramifications?

Question 21

What is reliability? (Precision)

Answer 21

• The degree to which the measurement yields a consistent value
• 5 systolic blood pressure readings yield 138, 140, 143, and 144 mmHg (mean = 141.25)
• +/- 6 mmHg in 4 measures? Good or not?
• Random measurement error is common and needs to be understood

Question 22

What is a population?

Answer 22

• Population (universe): all cases or observations of interest

Question 23

What is a sample?

Answer 23

Sample: a subset of cases or observations

Question 24

What is a sampling frame?

Answer 24

a list from which samples will be

selected

Question 25

What is a parameter?

Answer 25

characteristic of the population

Question 26

What is statistic?

Answer 26

characteristic of the sample

Question 27

Explain Canadian Health Measures Survey

Answer 27

• “aims to collect important health information through … interview … blood and urine”
• samples 3-79 yr olds in a nationally representative manner; approx. 5,000- 6,000/cycle
• 2-yr cycles, started 2007-2009
• Led by Statistics Canada, with Health Canada
and the Public Health Agency of Canada
• Direct physical measures, biospecimens

Question 28

Explain US NHANES Survey

Answer 28

• National Health and Nutrition Examination Survey
• “assess health and nutritional status”
• 1+yr old in a nationally representative manner; approx. 5,000-9,000/cycle
• Annual survey since 1971
• Blood Hg since 1999 (in children/female), and
2003-onwards in all participants
• Urine Hg also; Hg speciation also
• Led by National Center for Health Statistics

Question 29

Why CHMS Biomonitor?

Answer 29

• Establish reference ranges to enable deeper study of sub-populations or across countries
• Establish baseline levels to assess over-time changes
• Help set priorities and take action
• Assess effectiveness of regulatory decisions
• Support research on links between exposure and health effects