Comparative effectiveness of second line oral antidiabetic treatments among people with type 2 diabetes mellitus: emulation of a target trial using routinely collected health data by Bidulka, P, Lugo-Palacios, DG, Carroll, O, O’Neill, S, Adler, AI, Basu, A, Silverwood, RJ, Bartlett, JW, Nitsch, D, Charlton, P, Briggs, AH, Smeeth, L, Douglas, IJ, Khunti, K, Grieve, R