poses ▁trial ▁volunte ers ▁to ▁point less ▁risk ▁and ▁was tes ▁research ▁effort ▁( as ▁the ▁same ▁trial ▁is ▁repeated ▁over ▁and ▁over ). ▁It ▁also ▁bi ases ▁the ▁medical ▁literature , ▁making ▁it ▁report ▁effects ▁where ▁none ▁exist ▁( since , ▁given ▁enough ▁tri als , ▁eventually ▁one ▁will ▁find ▁a ▁difference ▁by ▁pure ▁chance ). ▁ ▁Pre - tri al ▁registration ▁makes ▁non - public ation ▁and ▁changes ▁in ▁analysis ▁methods ▁obvious ▁to ▁medical ▁review ers . ▁It ▁also ▁enables ▁authors ▁of ▁meta - stud ies ▁to ▁track ▁down ▁and ▁analy se ▁missing ▁data . ▁Finally , ▁it ▁lets ▁do ctors ▁and ▁patients ▁know ▁when ▁a ▁trial ▁is ▁looking ▁for ▁volunte ers . ▁ ▁There ▁are ▁other ▁sources ▁of ▁bias , ▁such ▁as ▁the ▁conditions ▁sometimes ▁attached ▁to ▁fund ing ▁by ▁fund ing ▁ag encies ▁with ▁a ▁financial ▁interest ▁in ▁the ▁trial ' s ▁outcome . ▁Medical ▁research ers ▁may ▁be ▁asked ▁to ▁agree ▁to ▁allow ▁the ▁fund ing ▁ag ency ▁to ▁c ensor ▁results . ▁Some ▁fund ing ▁ag encies ▁may ▁also ▁refuse ▁to ▁give ▁the ▁medical ▁research er ▁access ▁to ▁the ▁raw ▁data , ▁giving ▁them ▁only ▁the ▁finished ▁analysis , ▁or ▁even ▁a ▁draft ▁paper , ▁and ▁asking ▁them ▁to ▁put ▁their ▁name ▁to ▁it . ▁This ▁is ▁not ▁acceptable ▁academic ▁practice , ▁and ▁some ▁academic ▁journ als ▁require ▁that ▁authors ▁sign ▁a ▁statement ▁that ▁they ▁have ▁not ▁entered ▁into ▁such ▁agre ements . ▁ ▁Ben ▁Gold acre , ▁a ▁phys ician ▁and ▁sp ok esp erson ▁for