RT Journal Article SR Electronic T1 Ecological studies: use with caution JF British Journal of General Practice JO Br J Gen Pract FD British Journal of General Practice SP 65 OP 66 DO 10.3399/bjgp14X676979 VO 64 IS 619 A1 Catherine Saunders A1 Gary Abel YR 2014 UL http://bjgp.org/content/64/619/65.abstract AB