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“If a thing exists, it exists in some amount; and if it exists in some amount, it can be measured.” –E. L. Thorndike (1914)

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If a thing exists, it exists in some amount; and if it exists in some amount, it can be measured. E. L. Thorndike 19 - PowerPoint PPT Presentation

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“If a thing exists, it exists in some amount; and if it exists in some amount, it can be measured.” –E. L. Thorndike (1914). “If you haven\'t measured it you don\'t know what you are talking about.” -Lord Kelvin. Today’s Questions. What does it mean to measure a psychological variable?

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“If a thing exists, it exists in some amount; and if it exists in some amount, it can be measured.”

–E. L. Thorndike (1914)

today s questions
Today’s Questions
  • What does it mean to measure a psychological variable?
  • What is the difference between categorical and continuous variables, and why does the difference matter?
basic terminology
Basic Terminology
  • Variable: a characteristic that can vary or take on different values
    • Example: height is a variable
  • Value: a number representing one of many possible “states” of the variable
    • Example: some possible values of height are 6 feet or 4 feet 2 inches
  • Score: a specific value for a given person
    • Example: my score on the variable of height is 6 feet
systematic observation
Systematic Observation
  • In order to systematically observe something, it is critical to have a well-defined or quantitative system of measurement.
  • Simple example: How tall is Josh?
a more complex example
A More Complex Example
  • What about a question such as “How shy is Josh?”
  • This seems a bit more tricky because shyness, unlike height, isn’t something that we’re used to measuring with an everyday tool. It is a bit more abstract and elusive.
can psychological properties be measured
Can Psychological Properties be Measured?
  • However, there are two points worth considering.
    • Height isn’t exactly a “thing” in the way that a desk is a thing. Height, however, is an extremely useful abstraction. Is there any reason why shyness should be any more intractable than height?
    • There is nothing intrinsically concrete about inches, feet, miles, and meters. These are standard (i.e., conventional and agreed upon), but ultimately arbitrary, metrics.
can psychological properties be measured1
Can Psychological Properties be Measured?
  • Finally, we must address a common complaint: Psychological variables can’t be measured.
  • We regularly make judgments about who is shy and who isn’t; who is suffering and who isn’t; which marriages are functioning well and which are not
  • Implicit in these statements is the notion that some people are more shy, for example, than others
  • This kind of statement is inherently quantitative.
    • Quantitative: subject to numeric qualification.
interim summary
Interim Summary
  • Shyness, like distance, is a useful abstraction
  • We use the concept of shyness, like height, in quantitative ways (e.g., greater than, less than)
  • One goal of psychological measurement is to find standard and useful ways to systematically measure psychological constructs, such as shyness
  • An important first-step in measurement is determining whether a variable is categorical or continuous.
  • Why? This property of a variable determines how we quantify the variable, how we model its statistical behavior, and the way we analyze data regarding that variable.
nominal scale
Nominal Scale
  • With categorical, taxonic, qualitative, or nominal variables, people either belong to a group or they do not
  • Examples:
    • country of origin
    • biological sex (male or female)
    • animal or non-animal
    • married vs. single
  • Quantitative question: How many people belong to each category?
scales of measurement nominal scale
Scales of Measurement: Nominal Scale
  • Sometimes numbers are used to designate category membership
  • Example:

Country of Origin

1 = United States 3 = Canada

2 = Mexico 4 = Other

  • However, in this case, it is important to keep in mind that the numbers do not have numeric implications; they are simply convenient labels
continuous variables
Continuous Variables
  • With continuous variables, people vary in a graded way with respect to the property of interest
  • Examples:
    • age
    • working memory capacity
    • marital discord
  • Quantitative question: How much? or To what extent or degree?
scales of measurement continuous variables
Scales of Measurement: Continuous Variables
  • When we assign numbers to people (i.e., “scale” people) with respect to a continuous variable, those numbers represent something that is more meaningful than those used with nominal variables
  • Exactly what those numbers mean, and how they should be treated, however depends on the exact metric of the continuous variable...
scales of measurement ordinal
Scales of Measurement: Ordinal
  • Ordinal: Designates an ordering; quasi-ranking
  • Does not assume that the intervals between numbers are equal
  • Example:

finishing place in a race (first place, second place)

1st place

2nd place

3rd place

4th place

1 hour 2 hours 3 hours 4 hours 5 hours 6 hours 7 hours 8 hours

scales of measurement interval
Scales of Measurement: Interval
  • Interval: designates an equal-interval ordering
  • The distance between, for example, a 1 and a 2 is the same as the distance between a 4 and a 5
  • Example: Common IQ tests are assumed to use an interval metric
scales of measurement ratio
Scales of Measurement: Ratio
  • Ratio: designates an equal-interval ordering with a true zero point (i.e., the zero implies an absence of the thing being measured)
  • Example:
    • number of intimate relationships a person has had
      • 0 quite literally means none
      • a person who has had 4 relationships has had twice as many as someone who has had 2
scales of measurement additional comments
Scales of Measurement: Additional Comments
  • In general, most observable behaviors can be measured on a ratio-scale
  • In general, many unobservable psychological qualities (e.g., extraversion), are measured on interval scales
  • We will mostly concern ourselves with the simple categorical (nominal) versus continuous distinction (ordinal, interval, ratio)