  Deformation quantization produces families of mathematically equivalent
quantization procedures from which one must select the physically meaningful
ones. As a selection principle we propose that the procedure must allow enough
`observable' energy distributions, i.e., ones for which no pure quantum state
will appear with negative probability and must further have the property that
for these the uncertainty in the probability distribution of the quantum states
must not exceed that of the original distribution. For the simple harmonic
oscillator we show that this allows only the classic Groenewold-Moyal
(skew-symmetric) form.
