Kenyon, S;    Pike, K;    Jones, D;    Taylor, D;    Salt, A;    Marlow, N;    Brocklehurst, P;      (2005)    The effect of a monetary incentive on return of a postal health and development questionnaire: a randomised trial [ISRCTN53994660].                   BMC Health Services Research , 5     , Article 55.  10.1186/1472-6963-5-55 <https://doi.org/10.1186/1472-6963-5-55>.       Green open access