To cite feisr in publications please use:

  Rüttenauer T, Ludwig V (2020). Fixed Effects Individual Slopes:
  Accounting and Testing for Heterogeneous Effects in Panel Data or
  Other Multilevel Models Sociological Methods and Research.
  OnlineFirst. 10.1177/0049124120926211

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Fixed Effects Individual Slopes: Accounting and Testing for Heterogeneous Effects in Panel Data or Other Multilevel Models},
    author = {Tobias Rüttenauer and Volker Ludwig},
    year = {2020},
    journal = {Sociological Methods and Research},
    volume = {OnlineFirst},
    doi = {10.1177/0049124120926211},
    url = {https://osf.io/preprints/socarxiv/k4rnu/},
  }