Understand the subject
Why are there different kinds of mean?
Different means preserve different relationships. The arithmetic mean fits additive quantities; the geometric mean fits multiplicative factors; the harmonic mean fits certain rates; and root mean square emphasizes magnitude by squaring first.
For positive values, these four means always follow the same order—but that order does not decide which one answers your real question.
The relationship
The classical ordering of means
All four are equal only when every entered value is equal.
See the separation
The same values, four different centers
HarmonicRates over equal numerator-side exposure
GeometricMultiplicative factors and proportional change
ArithmeticAdditive values with equal influence
RMSMagnitude where signs should not cancel
Worked example
Compare the values 1 and 4
Each method processes the same two positive values through a different relationship.
H = 1.6 ≤ G = 2 ≤ A = 2.5 ≤ RMS = √8.5 ≈ 2.915
Interpret with care
Choose by meaning, not by size
The smallest or largest result is not automatically more conservative or more accurate. Identify what is being held equal—observations, multiplicative periods, distance or another exposure, or squared magnitude—before choosing a mean.
