Interval Scale Measurement

An interval scale does more than just rank data — it tells you exactly how far apart two measurements are, because the intervals between values are equal and meaningful. Temperature in Celsius or Fahrenheit is the classic example: the difference between $20^\circ$C and $30^\circ$C is the same as between $40^\circ$C and $50^\circ$C. However, the scale has no true zero point — $0^\circ$C does not mean "no temperature" — so ratios like "twice as hot" are meaningless. This property shapes which statistical measures you can legitim …