defining and measuring variables
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Defining and Measuring Variables. Slides Prepared by Alison L. O’Malley. Passer Chapter 4. Think of something that would not be considered a variable…. Variables: Qualitative vs. Quantitative. Qualitative Variable levels are categories – values reflect difference in kind - PowerPoint PPT PresentationTRANSCRIPT
Defining and Measuring Variables
Slides Prepared by Alison L. O’Malley
Passer Chapter 4
Think of something that would not be considered a variable…
Variables: Qualitative vs. Quantitative
•Qualitative •Variable levels are categories – values
reflect difference in kind •E.g., make of car, region of country
•Quantitative •Variable levels exist on a continuum from
low to high – values reflect difference in amount •E.g., number of siblings, quiz score
Variables: Discrete vs. Continuous
•Discrete• Intermediate values are impossible •E.g., # of cars owned, # of Oscars won
•Continuous• Intermediate values are possible – precision
limited only by our measurement tools •E.g., height (62.675... inches), weight • In practice, ultimately converted into
discrete values
The nature of our variables paves the way for how we make sense of them
Which type of variable is depicted in (a)? (b)?
Independent and Dependent Variables
Identify the independent variable and dependent variable in this research question:
Is aggressive behavior influenced by alcohol consumption?
Independent and Dependent Variables •Discuss independent and dependent variables in terms of “cause” and “effect” • Note that this causal language pertains only to
experimental research designs!
•Generate an example of an independent variable that cannot be manipulated
Constructs
Psychological scientists have their work cut out for them, as they tend to be interested in phenomena that are not directly observable.
Love? Motivation? Creativity?
Love? Motivation? Creativity?
Constructs
•Constructs must be translated into something measurable •This process occurs via operationalization•Generate an operational definition for aggression
Underlying Construct
Underlying Construct
Measurable Variable
Measurable Variable
Moderator Variables
•A moderator variable influences the direction and/or strength of the relationship between two variables
IV DV
Moderator
Moderator Variables •E.g., Social support moderates the relationship between stress and turnover•The relationship between stress and
turnover (i.e., leaving one’s job) is stronger when social support is low vs. when social support is high
Stress Turnover
Social Support
Mediator Variables
•Mediators explain a causal relationship, shedding light on the process by which the IV influences the DV
IV DVMediator
Mediator Variables
•Oishi, Kesebir, & Diener (2011) identified perceived fairness as a mediating variable accounting for the negative relationship between income inequality and happiness•High income inequality is associated with
low happiness due (in part) to low perceived fairness
Incomeinequality Happiness
Perceived fairness
Scales of Measurement
•Measurement: Assignment of numbers to aspects of objects or events according to rules
•Scale of measurement impacts how you analyze data
Scales of Measurement
•Nominal•Ordinal • Interval•Ratio
Least precise
Most precise
Scales of Measurement
•NominalGroup objects into categories Group objects into categories Variable levels differ in kind, not in degreeVariable levels differ in kind, not in degreeE.g., Political party affiliation E.g., Political party affiliation •Ordinal • Interval•Ratio
Scales of Measurement
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NominalNominalOrdinalOrdinal
Values reflect Values reflect rank rank orderingordering
1 hour 2 hours 3 hours 4 hours 5 hours 6 hours 7 hours 8 hours
1st place 2nd place 3rd place 4th place
Scales of Measurement
•Nominal•Ordinal • IntervalNumbers reflect actual amountsNumbers reflect actual amountsEqual distance between intervals Equal distance between intervals 0 point is arbitrary 0 point is arbitrary E.g., Temperature (in ° Celsius or E.g., Temperature (in ° Celsius or
Fahrenheit) Fahrenheit) Ratio
Scales of Measurement
•Nominal•Ordinal • Interval•RatioInterval scales, but zero point reflects true Interval scales, but zero point reflects true
absence of property absence of property Scores can be compared as ratios or Scores can be compared as ratios or
percentspercentsE.g., speed, dollars E.g., speed, dollars
Are Our Measures Any Good?
•Accuracy reflects the degree to which measure aligns with known standard
•What does accuracy have to do with systematic error (bias)?
Accuracy, Reliability, and Validity
Are Our Measures Any Good?
•Reliability refers to the consistency of measurement
•What does reliability have to do with random measurement error?
Accuracy, Reliability, and Validity
Are Our Measures Any Good?
•Several forms of reliability • Test-rest • Consistency of scores over time
• Internal consistency • Consistency of a measure within itself • Assumes multiple items – do the items
strongly correlate with each other?
Accuracy, Reliability, and Validity
Are Our Measures Any Good?
•Validity addresses the alignment between our construct and the measurement tool we employed to gain insight into the construct
•Like reliability, validity can be addressed in several ways
Accuracy, Reliability, and Validity
Are Our Measures Any Good?
•Face validity• Measure appears appropriate to participants • E.g., Job applicants perceived that an
interviewer asked job-relevant questions •Content validity • Measure adequately covers the domain of
interest• E.g., A course exam samples from all of the
content students were exposed to in and out of class
Accuracy, Reliability, and Validity
Are Our Measures Any Good?
•Criterion validity• Measure predicts an outcome • E.g., Conscientiousness is a
positive predictor of job performance
Accuracy, Reliability, and Validity
Are Our Measures Any Good?
John Pahn
Test 1
_____________________________
John Pahn
Performance Appraisal_________________________
Valid? (Correlated?)
Predictor CriterionJohn Pahn
Test 1
_____________________________
Jane Doe
Conscientiousness(Personality Test)
_____________________________
John Pahn
Test 1
_____________________________
Jane Doe
Job Performance Data
_____________________________
Establishing Criterion Validity
Are Our Measures Any Good?
•Construct validity • Measure authentically represents the
construct of interest • Demonstrated in part via convergent and
discriminant validity • Convergent example: Scores on new
creativity test correlate with scores on established creativity measures
• Discriminant example: Scores on new creativity test are not correlated with scores on an assertiveness measure • Creativity and assertiveness are different
constructs!
Are Our Measures Any Good?
• Scholars may differ in terms of how they approach validity and reliability, but they converge on the following ideas: • Reliability is a necessary but
insufficient condition for validity• Construct validity is the most
fundamental validity
Are Our Measures Any Good?
Consider a student who takes the SAT twice, and receives a much higher score the second time. Discuss this scenario in terms of accuracy, reliability, and validity.
Accuracy, Reliability, and Validity