Worker for this variable is usually a census definition based of economically active population.
For more information and proper citation see http://www.rug.nl/research/ggdc/data/pwt/pwt-7.1
Source Indicator: rgdpwok
Source: University of Pennsylvania
Release: Penn World Table 7.1
University of Pennsylvania, Purchasing Power Parity Converted GDP Chain per worker for Albania [RGDPWOALA627NUPN], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/RGDPWOALA627NUPN, February 6, 2016.