The incidence of child maltreatment may have been inaccurately reported due to inconsistency in the data from child protection agencies and variations in legislation from state to state, according to research published in the Medical Journal of Australia.

Researchers led by Dr Steven Guthridge from the Northern Territory's Department of Health and the University of Adelaide used hospital admissions data for children aged 0 to 17 years admitted to NT public hospitals between 1999 and 2010 to compare the incidence of child maltreatment with data from child protection services.

In the 12-year study period there were 313 admissions with at least one definitive diagnosis of maltreatment - 275 of whom were Aboriginal children and 38 were non-Aboriginal children. The average annual hospitalisation rate for definitive maltreatment diagnoses was 8.8 admissions per 10 000 per year for Aboriginal children and 0.91 for non-Aboriginal children.

For indicative maltreatment diagnoses - one or more diagnosis codes indicative of maltreatment - the rates of admission per 10 000 per year were 28.4 for Aboriginal children and 5.2 for non- Aboriginal children.

"Hospital admissions may provide a more consistent basis for comparison of rates of maltreatment between Australian states and territories than the current reliance on child protection reports", the researchers wrote.

In comparison with an earlier study by the same authors using child protection services data from 1999 to 2010, "the stable rate of maltreatment resulting in hospitalisation in younger Aboriginal children was in contrast to the increases in substantiated cases reported by child protection services".

"Through this period of legislative change, service expansion and continued media attention, the rate of substantiated cases of maltreatment increased by 18% per year among Aboriginal children, while there was no evidence of increase among non-Aboriginal children", Dr Guthridge and his coauthors wrote.

"We were unable to identify whether there had been a change in the underlying rates of maltreatment in the population."

The importance of epidemiologically informed methods for monitoring the occurrence of child maltreatment was highlighted in an editorial in the same issue of the MJA, written by Professor Graham Vimpani, professor of community child and family health at the University of Newcastle. "... reporting or notification and substantiation data from statutory child protection agencies ... are not good measures of the true prevalence of child abuse and neglect because they are subject to changes in legislation and reporting policies and practices", Professor Vimpani wrote.

"This is nowhere more evident than in the impact of the recent change to the reporting threshold in NSW, changed by legislation after the Wood Inquiry in 2008, from 'harm' to 'significant harm'. "The number of children who were the subject of a report increased steadily from the early 2000s, reaching 114 765 in the financial year 2008-09 before the NSW Government's Keep Them Safe reforms were introduced, but then falling to 61 132 in 2010-11."

The ideal system for true surveillance of child maltreatment "will need to link data from different sources - medical, legal and social service - and be maintained over time", Professor Vimpani wrote.

"This challenge reaffirms the growing recognition that 'wicked' problems like child maltreatment inevitably require high-level strategic leadership and the good will of many to devise a collective solution."