To cite gapclosing in publications use:

  Lundberg, Ian. 2021. The gap-closing estimand: A causal approach to
  study interventions that close disparities across social categories.
  Working paper. URL https://doi.org/10.31235/osf.io/gx4y3.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {The gap-closing estimand: A causal approach to study interventions that close disparities across social categories},
    author = {{Ian Lundberg}},
    journal = {Working Paper},
    year = {2021},
    url = {https://doi.org/10.31235/osf.io/gx4y3},
  }