1. 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

2. 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?

3. A More Complex Example What about something like “How shy is Fraley?” 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.

4. 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?

5. 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

6. 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.

7. 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

8. 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

9. 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?

10. Scales of Measurement: Nominal Scale Sometimes numbers are used to designate category membership Example: Country of Origin 1 = United States3 = Canada 2 = Mexico4 = Other However, in this case, it is important to keep in mind that the numbers do not have intrinsic meaning

11. 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

12. 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...

13. 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) 1 hour2 hours3 hours4 hours5 hours6 hours7 hours8 hours 1st place2nd place3rd place4th place

14. 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)

15. 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

16. 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) categoricalcontinuous ordinal interval ratio variables