/usr/lib/R/site-library/MCMCpack/CITATION is in r-cran-mcmcpack 1.3-3-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | citHeader("To cite MCMCpack in publications use:")
citEntry(entry = "Article",
  title        = "{MCMCpack}: Markov Chain Monte Carlo in {R}",
  author       = personList(as.person("Andrew D. Martin"), 
                   as.person("Kevin M. Quinn"), 
                   as.person("Jong Hee Park")),
  journal      = "Journal of Statistical Software",
  year         = "2011",
  volume       = {42},
  number       = {9},
  pages        = {1--21},
  url          = {"http://www.jstatsoft.org/v42/i09/"},
  textVersion  =
  paste("Andrew D. Martin, Kevin M. Quinn, Jong Hee Park (2011).",
        "MCMCpack: Markov Chain Monte Carlo in R.",
        "Journal of Statistical Software. 42(9): 1-21.",
        "URL http://www.jstatsoft.org/v42/i09/.")
)
 |