Chapter 12: Design Tools Flashcards
What is a variable?
• A factor or attribute that can assume two or more values
• Variables can vary
• Variability is wonderful in some cases but not
others – examples?
What is a domain?
- Domain is all possible values that a variable can have
* Smallest domain is two (dichotomous or binary)
What is a qualitative variable? Give examples
- properties that vary in a type of attribute
* Examples: sex, religion, eye color, marital status
What is a quantitative variable? Give examples
- Properties that different in an amount
* Examples: height, weight, blood pressure
What is a discrete variable?
• Quantitative adjacent variable in which no intermediate
values are possible
• Can we have 1.5 and 2.8 children?
What is a continuous variable?
• 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
What is an independent variable?
- Presumed causal factor in a cause-effect relationship
* In an experiment, this is what you manipulate (X-axis)
What is a dependent variable?
- Presumed effect in a cause-effect relationship
- “depends” upon the independent variable
- In an experiment, this is the outcome you measure (Y- axis)
What is mediator variable?
- X –> Mediator Variable –> Y
- Variable to explain why the two are linked…provides the CAUSAL link
- Fish Consumption –> ____________ –> IQ (+)
- Fish Consumption –> ____________ –> IQ (-)
What is moderating variable?
• (X --> Y) * moderator (M) • Variable that alters the strength or direction of the relationship • Aka interaction terms • (Fish Consumption --> IQ) * M
Mediator variable vs moderating variable
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.
What is confounding variable?
- Variable (C) that correlates with both X and Y
- Not in the causal pathway
- Causes confusion in the true relationship
What are conceptual and operational variables?
• 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
What are the 4 scales of measurement?
- nominal
- ordinal
- interval
- ratio
Define measurement
A process of systematically assigning values to variables
Define nominal scale and give examples
qualitative differences in scale values
• Sex, politics, college major, food categories, menu offerings, computer folders, hair color, birth city
• labels
Define ordinal scale and give examples
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
Define interval scale and give examples
Scale values have equal and exact distance
• Temperature, time of day, calendar year
Define ratio scales and give examples
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
What is accuracy (validity)?
- 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?
What is reliability? (Precision)
- 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
What is a population?
• Population (universe): all cases or observations of interest
What is a sample?
Sample: a subset of cases or observations
What is a sampling frame?
a list from which samples will be
selected
What is a parameter?
characteristic of the population
What is statistic?
characteristic of the sample
Explain Canadian Health Measures Survey
• “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
Explain US NHANES Survey
• 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
Why CHMS Biomonitor?
- 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
