Mechanical perception has been shown to follow the Weber-Fechner law, which states that the perceived intensity of a mechanical stimulus is proportional to the logarithm of the stimulus strength.
According to Mills et al (2012), it follows that when we test mechanical thresholds, we should be representing the withdrawal thresholds logarithmically, rather than linearly as most researchers do. Definitely check out this paper. It's well worth a read.
I now represent my PWTs in log(g) (with linear coordinates), rather than just as grams. I find that it makes my data tighter, and more importantly, as Mills argues, it makes the data more consistent with a normal distribution, which is a key underlying assumption of parametric stats (t-tests, ANOVAs, etc.). Truly, if we use PWTs in grams, we should be using non-parametric tests, although many pain papers don't do this.
So thinking logarithmically about PWTs has multiple benefits. What do you think? What do you do?
@jmogil, @fmoehring @ram_kandasamy