Hotaling, Straus, and Lincoln found that sibling aggression was somewhat common even in families that could not be classified as pervasively abusive, with 37% of 498 children committing at least one act of serious abuse during the previous year; in abusive families, 100% of children committed at least one act of serious abuse. Irfan and Cowburn report that in Pakistani immigrant families in the UK, "Among perpetrators of abuse, 35% (highest proportion) of physical abuse was perpetrated by siblings, 33% by mothers and 19% by fathers."