Multiverse analysis-a paradigm for statistical analysis that considers all
combinations of reasonable analysis choices in parallel-promises to improve
transparency and reproducibility. Although recent tools help analysts specify
multiverse analyses, they remain difficult to use in practice. In this work, we
conduct a formative study with four multiverse researchers, which identifies
debugging as a key barrier. We find debugging is challenging because of the
latency between running analyses and detecting bugs, and the scale of metadata
needed to be processed to diagnose a bug. To address these challenges, we
prototype a command-line interface tool, Multiverse Debugger, which helps
diagnose bugs in the multiverse and propagate fixes. In a second, focused study
(n=13), we use Multiverse Debugger as a probe to develop a model of debugging
workflows and identify challenges, including the difficulty in understanding
the composition of a multiverse. We conclude with design implications for
future multiverse analysis authoring systems