More information is available at http://pwt.econ.upenn.edu/Documentation/append61.pdf.
For proper citation, see http://pwt.econ.upenn.edu/php_site/pwt_index.php
Source Indicator: tcgdp
Source: University of Pennsylvania
Release: Penn World Table 7.1
University of Pennsylvania, Total Purchasing Power Parity Converted GDP, G-K method, at current prices for Tonga [PPPGDPTOA619NUPN], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/PPPGDPTOA619NUPN/, July 3, 2015.