Estimated changes in body mass index (difference in BMI) after October 2010 among nursery schoolchildren born between 2 April 2006 and 1 April 2007 in each affected prefecture versus unaffected prefectures in northeast Japan. Estimated changes in body mass index (difference in BMI) after October 2010 among nursery schoolchildren born between 2 April 2006 and 1 April 2007 in each affected prefecture versus unaffected prefectures in northeast Japan. Statistical tests evaluated the p values of the interaction terms in the model. *p<0.05, **p<0.01 and ***p<0.001. Hiroshi Yokomichi et al. BMJ Open 2016;6:e010978 ©2016 by British Medical Journal Publishing Group