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 ScaleNumber PropertiesPermissible RepresentedTransformations ----------------------------------------------------------------------- NominalSimilarities and differencesAny substitution that preserves the similarities and differences between the categories OrdinalSimilarities and differences,Any change the preserves rank orderorder among member IntervalSimilarities and differences,Addition of a constant, rank order, magnitude of multiplication by a differencespositive constant RatioSimilarities and differences,Multiplication by a rank order, magnitude ofpositive 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