Variables & Measurement Lesson 4

What are data? n Information from measurement l datum = single observation n Variables l Dimensions that can take on different values u IQ, height, shoe size, hair color l Is not the same for all individuals being measured ~

Measuring Variables n Operational definitions l Variables often abstract l Intelligence, anxiety, fitness, etc. l Need to objectively measure n Hypothesis: Salsa dancing increases fitness n Independent: Salsa dancing l Operational definition? n Dependent: fitness l Operational definition? ~

Levels of Measurement n Limits type of statistical analysis possible n Categorical variable l Discrete: only whole numbers l Frequency data u Number of instances that occur for a category n Continuous (quantitative) variable l represents magnitude l infinite number of values b/n adjacent scale values l Can be discrete: e.g., exam scores ~

Levels of Measurement: Categorical n Nominal scale l categorical l order NOT meaningful l can assign arbitrary values n Ordinal scale l Categorical + meaningful order l No info about magnitude of differences l If assign numerical value, must reflect order ~

Levels of Measurement: Quantitative n Interval scale (numbers) l Continuous or discrete l Equal intervals  equal differences n Ratio scale l same characteristics as interval l Ratios of values must be meaningful for magnitude l scale must have true zero point n Most statistics: interval/ratio treated the same ~

Levels of Measurement: SPSS n Variable view tab l Formatting of variable l Measure n Nominal scale n Ordinal scale n Scale l Interval & ratio n Reminder: IV must be nominal for most statistical tests ~

Measurement Error n Discrepancy l between actual value of observation and the reported value n Sources of measurement error l Sensitivity of measuring instrument l Conscientiousness of observer l Surveys: inaccurate or untruthful l Low reliability of instrument n  unsystematic variation ~

Reliability & Validity n Accurate measurement requires both n Reliability l Consistency of measurement n Criterion validity l Extent instrument actually measures what it claims to measure l Score on IQ test measures intelligence? l  pulse rate a measure of fear? n Important for internal & external validity ~