Beware the passenger card] Australian and New Zealand data on population movement between the two countries

"This article reports on idiosyncrasies of two official national migration databases, most of which became apparent when trying to account for marked differences in their estimates of both migratory and more short-term population movement between the two countries, and for variation over time in the pattern of differences. It is shown that the use of apparently similar broad classification principles, by different countries and through time within a country, can create impressions of comparability and continuity that may be quite misleading." Data are for Australia and New Zealand.