To cite the loo R package:

Vehtari A, Gabry J, Magnusson M, Yao Y, Gelman A (2019). “loo: Efficient leave-one-out cross-validation and WAIC for Bayesian models.” R package version 2.2.0, https://mc-stan.org/loo.

To cite the loo paper:

Vehtari A, Gelman A, Gabry J (2017). “Practical Bayesian model evaluation using leave-one-out cross-validation and WAIC.” Statistics and Computing, 27, 1413–1432. doi: 10.1007/s11222-016-9696-4.

To cite the stacking paper:

Yao Y, Vehtari A, Simpson D, Gelman A (2017). “Using stacking to average Bayesian predictive distributions.” Bayesian Analysis. doi: 10.1214/17-BA1091.

Corresponding BibTeX entries:

  @Misc{,
    title = {loo: Efficient leave-one-out cross-validation and WAIC for
      Bayesian models},
    author = {Aki Vehtari and Jonah Gabry and Mans Magnusson and Yuling
      Yao and Andrew Gelman},
    year = {2019},
    note = {R package version 2.2.0},
    url = {https://mc-stan.org/loo},
  }
  @Article{,
    title = {Practical Bayesian model evaluation using leave-one-out
      cross-validation and WAIC},
    author = {Aki Vehtari and Andrew Gelman and Jonah Gabry},
    year = {2017},
    journal = {Statistics and Computing},
    volume = {27},
    issue = {5},
    pages = {1413--1432},
    doi = {10.1007/s11222-016-9696-4},
  }
  @Article{,
    title = {Using stacking to average Bayesian predictive
      distributions},
    author = {Yuling Yao and Aki Vehtari and Daniel Simpson and Andrew
      Gelman},
    year = {2017},
    journal = {Bayesian Analysis},
    doi = {10.1214/17-BA1091},
  }