Are supplementary materials the new file drawer?

Supplementary materials have become a central feature of the contemporary onlinepublishing system, yet they remain largely overlooked by metascience research.I argue that supplementary materials should not be viewed as neutral side filespassively supporting the main document, but rather as motive-laden objects ca-pable of influencing the evaluation of scientific research. Specifically, the benefitsof supplementary materials may depend on the motives shaping their content. Whilesupplementary materials motivated by transparency may reduce publication biasand enhance readability, those driven by consistency motives risk becoming a newkind of file drawer. Indeed, these files offer optimal settings for spinning researchoutcomes by sorting information between the main document and supplementaryfiles to fit one’s narrative, making information technically available but effectivelyinvisibilised. Even if unintentional, and while distinct from questionable researchpractices such as selective reporting—where information is voluntarily omitted al-together—selectively presenting content between the main document and supple-mentary files has the potential to distort how research is perceived by stakeholders.I discuss the dual role of supplementary materials in promoting robust science andenabling spin, and how external constraints, such as word limits, may exacerbatethese dynamics. Finally, I propose ways to limit the negative impact of supplemen-tary materials through stronger justification, organisation, and control of informa-tion, and I consider opposing perspectives.