A monitoring system that may include an emission feature capable of emitting light into tissue, a modulator portion capable of modulating the emitter at a modulation frequency to generate photon density waves, a detection portion capable of detecting photons of the photon density waves after propagation through the tissue and capable of providing a distribution of detected photons over a time period for the photon density waves, and an analysis portion capable of calculating a skewness of the distribution and making determinations relating to a value of a physiologic parameter of the tissue based at least in part on the skewness of the distribution.