Historian Paul Moon writes of reports by missionaries of families forcing some of their young girls into the sex trade with the object of obtaining valuable and scarce English goods in the 1820s. He describes how, when a new ship arrived, the fathers came to take girls as young as 10 out of school. Moon records reports of widespread infanticide in Māori settlements—particularly the killing of baby girls, of slaves captured in battle or of half-caste children. Other historians such as Vincent O'Malley demonstrate that reports of this type are contradictory and often unreliable. Sam Ritchie points out that Moon fails to contextualize his interpretation of missionary writing and accepts it at face value without adequately considering other sources or the reasons behind such reports. Census figures in the 19th century showed a marked male/female imbalance throughout the North Island amongst Māori children. The 1857–8 Māori census recorded 32,329 males and only 23,928 females.