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The ManyBabies 1 project, a large-scale collaboration of developmental psychology labs to replicate a classic finding – infants' preference for infant-directed over adult-directed speech – provides a unique opportunity not only to take stock of the field and discover how our methods and approaches differ, but to being to understand the factors that make these effects so difficult to measure. Here, we are preregistering a plan to analyze additional variables collected alongside the main MB1 project, consisting of a wide range of 'lab factors' that researchers believe may impact either whether a baby fusses out of a study, or whether they truly attend to stimuli (and thus produce an expected effect in the study.) This is an exploratory project, designed to guide further research, but because of the size, sprawl, and uniqueness of this dataset, we aim to use it as well as possible, by pre-registering our analytic plan and, where possible, holding out part of the dataset to allow for confirmation of exploratory effects.