PT - JOURNAL ARTICLE ED - , TI - Correction AID - 10.1136/bmjopen-2013-002742corr1 DP - 2013 Jan 01 TA - BMJ Open PG - e002742corr1 VI - 3 IP - 6 4099 - http://bmjopen.bmj.com/content/3/6/e002742corr1.short 4100 - http://bmjopen.bmj.com/content/3/6/e002742corr1.full SO - BMJ Open2013 Jan 01; 3