Comparison of the effective collision strengths Υ_ij at 5000 K from CCC and BSR. The central dashed line shows the one-to-one relation, with the outer dashed lines showing factors of two and ten departures from this relation. Circled points are transitions involving the lowest five states of Mg. Points shown surrounded by a square are the transitions from the ground state to the two lowest-lying excited states, i.e. 3s–3s3p³P and 3s–3s3p¹P, the former always having a larger effective collision strength.