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Part II: Measuring Psychological Variables. In the last section, we discussed reasons why scientific approaches to understanding psychology may be useful A key concept was systematic observation. Systematic Observation.

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part ii measuring psychological variables
Part II: Measuring Psychological Variables
  • In the last section, we discussed reasons why scientific approaches to understanding psychology may be useful
  • A key concept was systematic observation
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 far is projector screen from the podium?
a more complex example
A More Complex Example
  • What about something like “How shy is Dr. Powell?”
  • This seems a bit more tricky because shyness, unlike distance, 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.
    • There is nothing intrinsically concrete about inches, feet, miles, and meters. These are standard (i.e., conventional and agreed upon), but ultimately arbitrary, metrics.
    • Distance isn’t exactly a “thing” in the way that a stool is a thing. Distance, however, is an extremely useful abstraction. Is there any reason why shyness should be any more intractable abstraction than distance?
can psychological properties be measured1
Can Psychological Properties be Measured?
  • A common complaint: Psychological variables can’t be measured.
  • We regularly make judgments about who is shy and who isn’t; who is attractive and who isn’t; who is smart and who is 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: It is subject to numerical qualification.
  • If it can be numerically qualified, it can be measured.
interim summary
Interim Summary
  • Shyness, like distance, is a useful abstraction
  • We use the concept of shyness, like distance, 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
  • An important first-step in measurement is determining whether a variable is categorical or continuous.
  • Why? This determines how we quantify or measure the variable.
  • Variable: A feature for which people differ.
    • Shyness: some people are more shy than others
    • Age: some people are older than others
nominal scale
Nominal Scale
  • With categorical, qualitative, or nominal variables people either belong to a group or 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 intrinsic meaning
continuous variables
Continuous Variables
  • With continuous variables, people vary in a graded way with respect to the variable
  • Examples:
    • age
    • intelligence
    • shyness
  • Quantitative question: How much or to what degree
scales of measurement continuous variables
Scales of Measurement: Continuous Variables
  • When we assign numbers to people (i.e., when we “scale” people) with respect to a continuous variable, those numbers represent something that is more tangible than those used in a nominal system.
  • Exactly what the numbers mean, and how they should be treated, however, depends on what kind of continuous metric we’re dealing with . . .
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
    • the difference between someone with a score is 120 and someone with a score of 100 is the same as the difference between people with scores of 80 and 60 (i.e., 20 points)
scales of measurement ratio
Scales of Measurement: Ratio
  • Designates an equal-interval ordering with a true zero point (i.e., the zero implies an absence of the thing being measured)
  • Example:
    • the 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)