Second Language Research Methods - Oxford Applied Linguistics:

Based on a set of four research parameters, this book discusses the development of research questions and hypotheses, naturalistic and experimental research, data collection, and validation of research instruments. Each chapter includes examples and activities.

socioeconomic status, job, educational aspirations, degree of ethnocentrism,
schooling, other second language experience,number of years of residence in
the second language environment, type of method used in teaching the language
, ...