N. P Zuithoff, Y Vergouwe, M King, I Nazareth, E Hak, K. G Moons and M. I Geerlings
Family Practice 26 ( 4 ): 241 - 250 , 2009
K. J Gorter, E Hak, N. P Zuithoff, A. I Hoepelman and G. E. Rutten
Family Practice 27 ( 4 ): 379 - 385 , 2010