Patients’ evaluations of patient safety in English general practices: a cross-sectional study by Ricci Cabello, I, Marsden, K, Avery, A, Bell, B, Kadam, U, Reeves, D, Slight, S, Perryman, K, Barnett, J, Litchfield, I, Thomas, S, Campbell, S, Doos, L, Esmail, A, Valderas, J