The general form of the law is where I is the intensity or strength of the stimulus in physical units (energy, weight, pressure, mixture proportions, etc.
A principal criticism has been that Stevens' approach provides neither a direct test of the power law itself nor the underlying assumptions of the magnitude estimation/production method: it simply fits curves to data points.
In addition, the power law can be deduced mathematically from the Weber-Fechner logarithmic function (Mackay, 1963[2]), and the relation makes predictions consistent with data (Staddon, 1978[3]).
In the context of axiomatic psychophysics, (Narens 1996) formulated a testable property capturing the implicit underlying assumption this assertion entailed.
This condition was confirmed for just over half the respondents, and the power form was found to be a reasonable approximation for the rest (Steingrimsson & Luce 2006).
It has also been questioned, particularly in terms of signal detection theory, whether any given stimulus is actually associated with a particular and absolute perceived intensity; i.e. one that is independent of contextual factors and conditions.