Authors’ contributions
All authors were involved in drafting the article or revising it critically for important intellectual content. All authors approved the final version to be published. Ms Spekking and dr Hissink Muller had full access to all data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design: KS, PB, SB, DB, CA, RC, LS, MR, PHM. Acquisition of data: PHM, DB, CA, DS, YK, MR, LS, MB. Critically revising the manuscript; KS, JA, PB, SB, MB, DS, YK, MR, LS, CA, RC, DB, PHM.