To cite ptmixed in publications use:

Signorelli M, Spitali P, Szigyarto CA, Consortium TM, Tsonaka R (2021). “Penalized regression calibration: A method for the prediction of survival outcomes using complex longitudinal and high-dimensional data.” Statistics in Medicine. https://doi.org/10.1002/sim.9178.

Corresponding BibTeX entry:

  @Article{,
    title = {Penalized regression calibration: A method for the
      prediction of survival outcomes using complex longitudinal and
      high-dimensional data},
    author = {M. Signorelli and P. Spitali and C. Al-Khalili Szigyarto
      and The MARK-MD Consortium and R. Tsonaka},
    journal = {Statistics in Medicine},
    year = {2021},
    url = {https://doi.org/10.1002/sim.9178},
  }