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Referee Comments: Referee 3

Posted by PLOS_ONE_Group on 01 May 2008 at 14:18 GMT

Referee 3's review:

N.B. These are the comments made by the referee when reviewing an earlier version of this paper. Prior to publication, the manuscript has been revised in light of these comments and to address other editorial requirements.

Review of the original submission:
This is in an interesting manuscript, in which the authors use "waiting time statistics" of active and resting periods in both human and mouse activity measurements to show that both species show similar classes of probability distributions. Moreover, by examining mutant mice the authors find changes in this distribution that are similar to those obseved in subjects with depression. The authors conclude that assessing these statistics one is able to capture important information about alteration in healthy behaviors

This manuscript has several strengths:
(1) use of a well established approach in physics to biological data
(2) ability to quantify complex behavioral patterns into classes of behavior
(3) ability to draw analogies between different species

There are some significant weaknesses:
(1) the statistical section is inadequate, the authors do not state when they select a power law function and when they select a stretched exponential function and what statistics they use to select one over the other.
(2) although there is a statistical similarity across species and it is of interest that rest and activity follow a certain statistical law, it is somewhat disappointing that there is not more of an effort to gain a deeper and possibly mechanistic understanding of what drives the system to behave in such a way.
(3) the parametric manipulations (changes of scale and time) are inadequate and merely qualitatively described. The authors should attempt to specifically develop a quantitative method to argue for the ranges of scales that are being considered here.

Review of the first revised manuscript:
The authors have significantly revised the previous manuscript and extended the statistical analysis section. At this time, I have no further concerns. This manuscript clearly extends work of previous investigators and makes important contributions to understanding the temporal characteristics of animal and human locomotor behavior.