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: rgdpl2wok
Source: University of Pennsylvania
Release: Penn World Table 7.1
University of Pennsylvania, Purchasing Power Parity Converted GDP Laspeyres per worker for Iceland [RGDPLWISA627NUPN], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/RGDPLWISA627NUPN, February 13, 2016.