Notes Exams are graded People did very well

Notes • Exams are graded. People did very well. Exams will be distributed in labs this week. • Our lab this week will be on Thursday.

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 Fraley from the back of the room?

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.

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 or concept. 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. • Important point: 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 personality assessment 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 which may differ across people. – 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 • The 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 2 = Mexico 3 = Canada 4 = Other • However, in this case, it is important to keep in mind that the numbers do not have intrinsic meaning. They are simply labels.

Continuous Variables • With continuous variables, people vary in a graded way with respect to the variable in question. • Examples: – age – intelligence – shyness • Quantitative questions: 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) 1 st place 1 hour 2 hours 2 nd place 3 rd place 3 hours 4 th place 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 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