What is a Measurement?

1. What is a Measurement? • Concept of measurement is intuitively simple • Measure something two concepts involved • The thing you are measuring • The measurement you produce • A Measurement is the relation between a system of labels and the property of an empirical object or event • Ex, A ruler

2. What is a Measurement?, con’t • Constructs and observations • Problem: Sometimes the property you wish to measure cannot be observed directly • Construct: Abstract properties of things that cannot be measured directly • Conceptual or theoretical variables

3. What is a Measurement?, con’t • Variables and variability • A variable is anything that can vary • Measure property in different objects under different conditions • If you the same answer, not measuring a variable • If you get different answers, you are measuring a variable • Variability is name for differences in measurements of property • Sources of variability are factors that can cause differences

4. What is a Measurement?, con’t • Variables and variability, con’t • When you measure a construct, the result depends on things other than the construct you’re measuring • Measurement may respond to irrelevant values • Measurement may be affected by random factor • True value + Irrelevant value + Random Error = Measurement

5. What is a Measurement?, con’t • Operational definitions • Specification of exactly what steps or operations are conducted to arrive at a particular measurement • Converging operations

6. Levels of Measurement • Nominal measurements • Put names into categories • Don’t contain any information about the amount of a property • Ordinal measurements • Specifies the order of items being measurement • Symbols typically numbers, but not always • (Equal) Interval measurements • Categories ordered by amount of property they have • Can add or subtract, but cannot multiply or divide • Ratio measurements • Interval scale with a true zero point • Can add and subtract, and multiply and divide

7. Levels of Measurement, con’t Comparison of the scales Scale Number Properties Permissible Represented Transformations ----------------------------------------------------------------------- Nominal Similarities and differences Any substitution that preserves the similarities and differences between the categories Ordinal Similarities and differences, Any change the preserves rank order order among member Interval Similarities and differences, Addition of a constant, rank order, magnitude of multiplication by a differences positive constant Ratio Similarities and differences, Multiplication by a rank order, magnitude of positive constant differences, ratios of properties between individuals, meaningful zero point

8. How Good is the Measurement? • Reliability • A measure has high reliability if it gives the same result every time the property is measured in the same way • How to determine reliability • Test – Retest reliability • Split – Half reliability • Alternate form reliability • Interrater reliability

9. How Good is the Measurement?, con’t • Validity • A measure has validity when it reflects the construct you intend it to measure • Types of validity • Face validity • Criterion validity • Current validity • Predictive validity • Content validity • Construct validity • Internal validity