Citing the studies on the regression hypothesis that have been done, Yukawa (1998) says that the results have been contradictory. It is possible that attrition is a case-by-case situation depending on a number of variables (age, proficiency, literacy, the similarities between the L1 and L2, and whether the L1 or the L2 is attriting). The threshold hypothesis states that there may be a level of proficiency that once attained, enables the attriting language to remain stable.

झीज आणि उपयोगाची वारंवारता frequency
भाषा झीजेचे प्रकटीकरन
L2
Other studies on bilingualism and attrition