measurement theory

Houle D, Pélabon C, Wagner GP & Hansen TF 2011 Measurement and meaning in biology. Q Rev Biol 86:3-34.

• Wagner (2010) showed that Wrightian fitness, w, is a ratio-scale measure under the assumption that the time scale is fixed
• we relax this assumption here because conclusions about fitness can be drawn on any time scale
• fitness, therefore, becomes a log-interval-scale variable, as the conclusions are invariant to power transformations of fitness

• the Malthusian parameter m measures fitness in continuous time
• the biological meaning of the fitness measures is contained in the differences of the fitness values, rather than the ratios
• thus m is an interval-scale variable
• only the differences between ms have evolutionary meaning
• neither the sign nor the absolute magnitude is meaningful for evolution
• they have ecological meaning as growth rates