  Throughout quantum mechanics there is statistical balance, in the collective
response of an ensemble of systems to differing measurement types. Statistical
balance is a core feature of quantum mechanics, underlying quantum mechanical
states, and not yet explained. The concept of "statistical balance" is here
explored, comparing its meaning since 2019 with its original meaning in 2001.
Statistical balance now refers to a feature of contexts in which: (a) there is
a prescribed probability other than 0 or 1 for the collective response of an
ensemble to one measurement type; and (b) the collective response of the same
ensemble to another measurement type demonstrates that no well-defined value
can be attributed, for the property relevant to the original measurement type,
to individual members of the ensemble. In some unexplained way, the outcomes of
single runs of a measurement of the original type "balance" each other to give
an overall result in line with the prescribed probability. Unexplained
statistical balance prompts caution in assessing the conceptual implications of
entanglement, measurement, uncertainty, and two-slit and Bell-type analyses.
Physicists have a responsibility to the wider population to be conceptually
precise about quantum mechanics, and to make clear that many possible
conceptual implications are uncertain.
