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 Origin1 = 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. 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 hour 2 hours 3 hours 4 hours 5 hours 6 hours 7 hours 8 hours

1st place 2nd place 3rd place 4th place

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).

categoricalcategorical continuouscontinuous

ordinalordinal

intervalinterval

ratioratio

variablesvariables