The default separation for the distinguishing and consensus
probabilities: the reliability-adjusted critical difference used to
flag distinguishing statements in classical Q analysis (Brown 1980;
Zabala & Pascual 2016), here generalized by computing it from the
posterior dominant-factor counts. With p_f the number of
participants whose posterior dominant factor is f,
r_f = p_f r0 / (1 + (p_f - 1) r0) and SE_f = sqrt(1 - r_f),
delta = z * mean_{k < l} sqrt(SE_k^2 + SE_l^2). The reliability is
the stable population reliability of the design, not the posterior
estimation spread.