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. 2019 Oct 7;9(10):e030213. doi: 10.1136/bmjopen-2019-030213

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© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY. Published by BMJ.

This is an open access article distributed in accordance with the Creative Commons Attribution 4.0 Unported (CC BY 4.0) license, which permits others to copy, redistribute, remix, transform and build upon this work for any purpose, provided the original work is properly cited, a link to the licence is given, and indication of whether changes were made. See: https://creativecommons.org/licenses/by/4.0/.

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Flowchart of sample. CIN,Children In Need; CLA, Children Looked-After; FSM, free school meals; GCSE, General Certificate of Education; KS4, Key Stage 4; NPD, National Pupil Database; SEN, special educational needs.