1Woods, A. , Fletcher, P. & Hughes, A.. Statistics in Language Studies[ M ]. Chambridge: Cambridge University Press, 1986.
2Buher, C. Statistics in Linguistics[ M ]. Oxford : Basil Blackwell, 1985.
3Ferris, M.R. & Politzer, RL L. Effects of early and delayedsecond language acquisition: English composition skill of Spanish -speaking junior high school students [ J]. TESOL Quarterly 15,1981.