defining and measuring variables

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Defining and Measuring Variables Slides Prepared by Alison L. O’Malley Passer Chapter 4

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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 Presentation

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Page 1: Defining and  Measuring  Variables

Defining and Measuring Variables

Slides Prepared by Alison L. O’Malley

Passer Chapter 4

Page 2: Defining and  Measuring  Variables

Think of something that would not be considered a variable…

Page 3: Defining and  Measuring  Variables

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

Page 4: Defining and  Measuring  Variables

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

Page 5: Defining and  Measuring  Variables

The nature of our variables paves the way for how we make sense of them

Which type of variable is depicted in (a)? (b)?

Page 6: Defining and  Measuring  Variables

Independent and Dependent Variables

Identify the independent variable and dependent variable in this research question:

Is aggressive behavior influenced by alcohol consumption?

Page 7: Defining and  Measuring  Variables

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

Page 8: Defining and  Measuring  Variables

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?

Page 9: Defining and  Measuring  Variables

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

Page 10: Defining and  Measuring  Variables

Moderator Variables

•A moderator variable influences the direction and/or strength of the relationship between two variables

IV DV

Moderator

Page 11: Defining and  Measuring  Variables

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

Page 12: Defining and  Measuring  Variables

Mediator Variables

•Mediators explain a causal relationship, shedding light on the process by which the IV influences the DV

IV DVMediator

Page 13: Defining and  Measuring  Variables

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

Page 14: Defining and  Measuring  Variables

Scales of Measurement

•Measurement: Assignment of numbers to aspects of objects or events according to rules

•Scale of measurement impacts how you analyze data

Page 15: Defining and  Measuring  Variables

Scales of Measurement

•Nominal•Ordinal • Interval•Ratio

Least precise

Most precise

Page 16: Defining and  Measuring  Variables

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

Page 17: Defining and  Measuring  Variables

Scales of Measurement

17

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

Page 18: Defining and  Measuring  Variables

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

Page 19: Defining and  Measuring  Variables

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

Page 20: Defining and  Measuring  Variables

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

Page 21: Defining and  Measuring  Variables

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

Page 22: Defining and  Measuring  Variables

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

Page 23: Defining and  Measuring  Variables

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

Page 24: Defining and  Measuring  Variables

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

Page 25: Defining and  Measuring  Variables

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

Page 26: Defining and  Measuring  Variables

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

Page 27: Defining and  Measuring  Variables

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!

Page 28: Defining and  Measuring  Variables

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

Page 29: Defining and  Measuring  Variables

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