Appearance-Disappearance Relation in 3+N_(s) Short-Baseline Neutrino Oscillations

We derive the relation between the amplitudes of short-baseline appearance and disappearance oscillations in 3+$N_{s}$ neutrino mixing schemes which is the origin of the appearance-disappearance tension that is found from the analysis of the existing data in any 3+$N_{s}$ neutrino mixing scheme. We illustrate the power of the relation to reveal the appearance-disappearance tension in the cases of 3+1 and 3+2 mixing using the results of global fits of short-baseline neutrino oscillation data.