Usability Testing of Mobile Applications: A Comparison between Laboratory and Field Testing
http://www.usabilityprofessionals.org/upa_publications/jus/2005_november/mobile.pdf
  peer-reviewed

Kaikkonen, Anne, Aki Kekäläinen, Mihael Cankar, Titti Kallio and Anu Kankainen
Journal of Usability Studies
2005

Abstract:

Usability testing a mobile application in the laboratory seems to be sufficient when studying user interface and navigation issues. The usability of a consumer application was tested in two environments: in a laboratory and in a field with a total of 40 test users. The same problems were found in both environments, differences occurred in the frequency of findings between the contexts. Results indicate that conducting a time-consuming field test may not be worthwhile when searching user interface flaws to improve user interaction. In spite of this, it is possible that field testing is worthwhile when combining usability tests with a field pilot or contextual study where user behavior is investigated in a natural context.