  Switching current distributions have for decades been an indispensable
diagnostic tool for studying Josephson junctions. They have played a key role
in testing the conjecture of a macroscopic quantum state in junctions at
millikelvin temperatures. The conventional basis of the test has been the
observation of temperature independence of SCD peak widths, and that led to
affirmative conclusions about a crossover. A different criterion is proposed
here - the distance of the SCD peak from the junction critical current - and
its efficacy is demonstrated. This test has distinct advantages in terms of
precision, and it is found that, for three example experiments, the evidence
for a crossover to the conjectured macroscopic quantum state is unequivocally
negative. The implications of this finding for superconducting qubits are
considered.
