It says in the article (or in the linked article which covers the same ground). It's tests like the "unsafe situation": a baby is put in peril, and the mother

It says in the article (or in the linked article which covers the same ground). It's tests like the "unsafe situation": a baby is put in peril, and the mother has to reassure it. Babies that are quickly reassured typically do better overall, and this is seen as a sign of strong bond. But fathers traditionally score low on this test (as babies appear to prefer the mothering parent for such reassurance)