2. Scales (levels) of Measurement
To determine level of measurement
• Step #1Identify the Unit of Observation
(obs unit) (sampling unit)
– (one of something)
• What you are interested on studying?
• Usually the individual (participant) for psychologists
• Other possible Observational units:
– A rat
– A Group/team
– A Household
– A City
– A Country
– A College student
3. Scales (Levels) of Measurement
To determine level of measurement
• Step #2 Ask: “What am going to do with the Obs unit?”
– Two options:
• Option A: Assign the Obs unit to a category (quality)
– E.g. gender, race, social security number (unique)
• Option B: Measure the Obs unit on some attribute or behavior
– Intelligence, age, motivational level, number of hotdogs eaten
– If “Yes” to Option A
• Ask: are the categories ranked on some quality?
– E.g. job class (clerical I, II, III)
– E.g. class standing (rank in class)
• If “NO”, not ranked, then level of measurement is NOMINAL
• If “Yes”, categories ranked, level of measure is ORDINAL
4. Scales (Levels) of Measurement
To determine level of measurement
• If Option B: Measure Obs Unit on some attribute or
behavior
• Step #3 Identify Unit of Measure (Measurement Unit)
– One of something (attribute or behavior)
• E.g. item on a test, inventory
– Ask: “Does the measure have a true zero? Usually:
• Physical and behavioral ones do
– E.g height, weight, number of cases sold
• Psychological attributes do not
– IQ, need for approval, depression level, attitude toward boss
5. Scales (Levels) of Measurement
To determine level of measurement
• If answer to “Does the measure have a true zero?”
– Is “YES”, level is Ratio
– Is “No”, level is Interval
• Try out a few:
6. What level (scale)?
Number of children aboard each of 15 school buses?
• Observational unit?
– One school bus
• Place bus in category?
– No
• Measurement Unit?
– One student
• Absolute zero?
– Yes, bus could carry no students
• Level of measure?
– Ratio
7. What Level Measurement?
Students Fail v. Pass
• Observational unit?
– One student
• Place student in category?
– Yes: fail or pass
• Are the categories ranked on some quality?
– Yes (underlying continuous variable…success in learning)
• Level of measurement?
– Ratio
– Just kidding!
– Ordinal
