Another limitation of the study is that those not educated within the state system were not involved with the NCMP and so it was not possible to consider those who were home or privately educated. There were

some differences in the characteristics of the sample analysed for this study compared with that analysed by Procter et al. (2008); notably Devon is much less ethnically OSI-744 diverse than Leeds. However, the similarity between our findings within any year, and those of Procter et al. (2008) would suggest that the methods employed were not sensitive to differing sample characteristics and hence the approach has some external validity. The problems associated with the reliability of league tables are well documented (Goldstein and Spiegelhalter, 1996 and Marshall and Spiegelhalter, 1998) and yet they remain in regular use in health, education and other areas of political interest (Marshall et al., 2004). Marshall and Spiegelhalter (1998) in examining in vitro fertilisation clinics found that ‘[e]ven when there

are substantial differences between institutions, ranks are extremely unreliable statistical summaries of performance and change in performance’ (p. 1701). Phenomena such as regression towards the mean are responsible for the instability of league tables and control chart methods have been proposed as a more robust alternative ( Marshall et al., 2004). Further work is needed to establish whether control charts could reliably identify schools which are ‘hot’ and ‘cold’ spots for obesity. However, the failure to find patterns among the rankings of individual schools over the five years studied indicates that individual

GSK1210151A datasheet schools were not differentially affecting pupil weight status, suggesting that school-based ‘hot’ and ‘cold’ spots for obesity may not exist and therefore are not appropriate targets for resources. In conclusion, this study found that estimates of individual school impacts on pupil weight status were small and labile across Endonuclease the five-year study period, refuting the hypothesis of a systematic differential impact of primary schools on pupil weight status. Furthermore, this suggests that ranking schools into ‘obesogenic league tables’ using current value-added methods is not a reliable approach to the identification of schools requiring targeted resources. As with previous studies (e.g. Harrison et al., 2011 and Townsend et al., 2012), only a small proportion of the variation in pupil weight status was found to be attributed to schools (Table 1). The marked changes in the impact of individual schools on pupil weight status from year-to-year bring into question whether the argument that small population level changes can reflect significant changes for individuals, proposed by Rose and Day (1990) is still a valid justification for school-based obesity prevention. It would appear that interventions intended to affect pupil weight status need to influence the wider environment and not just the school in isolation.