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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

- 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

- 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?

- 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 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.

Quantitative

- 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

- 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

Quantification

- 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

- 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

- 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

- 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

- 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

- 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

- 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

- 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

- 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)

variables

categorical

continuous

ordinal

interval

ratio

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