1. Measurement is the foundation of scientific investigation and involves assigning numbers or symbols to characteristics of objects.
2. There are four levels of measurement: nominal, ordinal, interval, and ratio. Nominal involves classification while ordinal captures ordering. Interval captures equal distances between intervals and ratio includes having a true zero point.
3. Reliability and validity are important for ensuring measurements accurately capture the construct being measured. Reliability looks at consistency over time, across items, and between raters. Validity compares measurements to conceptual definitions and whether scores relate to other expected outcomes.