http://www.essex.ac.uk/langling/documents/elct/2013/esperanto_tool.pdf
The early research that does exist (e.g. Fisher, 1921; Halloran, 1952, Williams, 1965a, 1965b) is reported in brief terms and thus does not pass today’s quality standards
Also explains why there’s no copy online.
http://www.essex.ac.uk/langling/documents/elct/2013/esperanto_tool.pdf
Also explains why there’s no copy online.