Authorship and acknowledgements.

All persons designated as authors of a scientific manuscript should qualify for authorship, and all those who qualify should be listed. Each author should have participated sufficiently in the work to take public responsibility for appropriate portions of the content, and have made substantial intellectual contribution to the submitted manuscript. All contributors who do not meet the criteria for authorship should be listed in the acknowledgements section. Ghost authors are undesirable while professional medical writers are helpful to authors who are not native English speakers, have language difficulties, or lack training or expertise in medical writing.