File image Photo: Unsplash / Jelleke Vanooteghem The research, published in the Medical Journal, is based on data collected as part of the 40-year Christchurch Health and Development Study, which has followed more than 1000 participants since they were born in 1977. In this study, University of Otago researchers tracked participants who were parents over a 15-year period between 2002 and 2017, when they were aged between 25 and 40, and collected information about how they disciplined their children. Researchers found minor assaults against children reduced over that time by almost half, from 77 percent to 42 percent. Severe assaults decreased by two-thirds, from 12 percent In 2007, the anti-smacking law came into effect but researcher Geraldine McLeod said it was difficult to say whether it was a big factor in the decline.