When using pwt9 in publications, please cite both the pwt9 package and the Penn World Table itself:

Zeileis A (2019). pwt9: Penn World Table (Version 9.x). R package version 9.1-0, https://CRAN.R-project.org/package=pwt9.

To cite the Penn World Table (version 9.x), please use:

Feenstra RC, Inklaar R, Timmer MP (2015). “The Next Generation of the Penn World Table.” American Economic Review, 105(10), 3150–3182. http://www.ggdc.net/pwt/.

Corresponding BibTeX entries:

    title = {pwt9: Penn World Table (Version 9.x)},
    author = {Achim Zeileis},
    year = {2019},
    note = {R package version 9.1-0},
    url = {https://CRAN.R-project.org/package=pwt9},
    title = {The Next Generation of the Penn World Table},
    author = {Robert C. Feenstra and Robert Inklaar and Marcel P.
    year = {2015},
    journal = {American Economic Review},
    volume = {105},
    number = {10},
    pages = {3150--3182},
    url = {http://www.ggdc.net/pwt/},