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: rgdptt
Source: University of Pennsylvania
Release: Penn World Table 7.1
University of Pennsylvania, Purchasing Power Parity Converted Gross Domestic Income (adjusted for Terms of Trade changes) for Sierra Leone [RGDPTTSLA625NUPN], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/RGDPTTSLA625NUPN/, July 30, 2015.