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 • 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

Part II: Measuring Psychological Variables