Level of measurement

Categories proposed by S. S. Stevens

Levels

Nominal

• Operations: $=$, $\ne$
• Central tendency: Mode (statistics)
• Variability: Qualitative variation

Ordinal

• Operations: ,
• Central tendency: Median
• Variability: Range, Interquartile range

Interval

• Operations: $+$, $-$
• Central tendency: Arithmetic mean
• Variability: Deviation

Ratio

• Operations: $\times$, $÷$
• Central tendency: Geometric mean, Harmonic mean
• Variability: Coefficient of variation, Studentized range

See also

• Nominal, ordinal, interval, and ratio typologies are misleading