MEASUREMENT the process of determining the value or level of a particular CONSTRUCT for every unit of analysis or subject involves OPERATIONALIZATION –translating an intangible concept into one or more tangible properties that can be observed and measured. (product is a VARIABLE) The most difficult constructs to measure???

*****Remember***** there will normally be a number of alternative ways to operationalize a concept even the best measure normally is only a REPRESENTATION of the underlying concept and is often an imperfect representation. –e.g. IQ or GNP

Basic Assessment Criteria TYPE of measurement scale VALIDITY of measurement system RELIABILITY of measurement system

Type of measurement scale (kind of system used to assign values to cases)

Nominal Scales creating a classification system qualitative distinctions (occupation) Numbers may be assigned to each group but the numbers are only LABELS can perform some quantitative analysis. –E.g. count frequencies of categories

Ordinal Scales first level of quantitative numbers are more than labels ordinal categorical vs. totally ordered numbers do not provide info. on the size of the difference between scale categories (how much higher)

Interval Scales Specify the exact amount of the measured characteristic that is present (e.g. years of formal education; yearly income) result: give info. about the size of the gap between all subjects on the scale

Significance of Type or Level of Measurement??? the type of measurement of a data set constraints the statistical analysis you can perform on that data set think of as a HIERARCHY –INTERVAL--can treat as if: ordinal or nominal –ORDINAL--can treat as if: nominal –NOMINAL

Exception: Dichotomous scales (nominal scales with only 2 categories) --- for many purposes the numerical values can be treated as though they were interval scale values---

Validity vs. Reliability validity –the measuring instrument is actually measuring the concept in question, not some other concept –it is doing so accurately reliability –consistency of measurement--produces the same outcome time after time. But not necessarily the right outcome

Ways of assessing validity content (or face) validation criterion validation construct validation

Ways of assessing reliability in the context of questionnaires split-half method test-retest parallel forms