criticalWeight

The weight on metric at which alternatives a and b change places, or null when they never do.

Null covers several situations, all of which mean the same thing to a caller: there is no weight in 0, 1 at which the order of these two changes. That happens when the metric already carries all the weight, so there is nothing to redistribute; when the study has only one metric, so its weight is fixed at one; when the two alternatives keep a constant gap however the weight moves; and when the crossing exists mathematically but lies outside the range a weight can take.