To cite brokenstick in publications use:

van Buuren S (2023). “Broken Stick Model for Irregular Longitudinal Data.” Journal of Statistical Software, 106(7), 1–51. doi:10.18637/jss.v106.i07.

Corresponding BibTeX entry:

  @Article{,
    title = {Broken Stick Model for Irregular Longitudinal Data},
    author = {Stef {van Buuren}},
    journal = {Journal of Statistical Software},
    year = {2023},
    volume = {106},
    number = {7},
    pages = {1--51},
    doi = {10.18637/jss.v106.i07},
  }