Hans Schepers wrote:
> To my biological viewpoint, only the fractional
> form is correct, since it does not make any sence
> to take a logarithm (or any other transcendental function)
> of a non-dimensionless quantity.
In my view, this is a very weak argument. Formally it may not be correct to
take logarithms of quantities with dimensions, but of course it is very
common shorthand in science, for example in thermodynamic and kinetics
applications. Any objection can be worked around by using quantities
relative to some defined state (e.g. 1M for concentrations ...). The
difference about this normalisation is that the answer does not change
depending on your choice of reference state for normalisation, unlike the
fractional change form which does. Of course, this independence of the
actual reference state chosen in the logarithmic version exactly illustrates
why it is not very important to worry about converting to relative measures.
Would anyone seriously object to using a logarithmic plot to study an
exponential growth of biomass on the grounds that you can't take logs of a mass?
David Fell
=========================================================
David Fell,
School of Biological & Molecular Sciences,
Oxford Brookes University,
Oxford OX3 0BP, Tel. +44 (0)1865 483247
UK FAX +44 (0)1865 484017
daf at bms.brookes.ac.uk
See my book at: http://www.portlandpress.co.uk/books/isbn/185578047X.htm
