Andrew D. Cohen & Susan M. Gass 
Research Methodology in Second-Language Acquisition [PDF ebook] 

This volume addresses salient theoretical issues concerning the validity of research methods in second-language acquisition, and provides critical analysis of contextualized versus sentence-level production approaches. The contributors present their views of competence versus performance, the nature of language acquisition data, research design, the relevance of contextualized data collection and interpretation, and the desirability of a particularistic nomothetic theoretical paradigm versus more comprehensive consideration of multiple realities and complex influencing factors. This book presents varying and antithetical approaches to the issues, bringing together the thinking and approaches of leading researchers in language acquisition, language education, and sociolinguistics in an engaging debate of great currency in the field.