Rang, O., & Moran, M. (2014). Functional Loads of Pronunciation Features in Nonnative Speakers’ Oral Assessment. TESOL Quarterly, 48(1), 176-187. Retrieved from www.jstor.org/stable/43267954
In the research world of applied linguistics and English language teaching, there is a term called functional loads, which ranks phonemic errors and features to give a hierarchy of “worse” and “better” errors to have because they impact a listeners’ comprehension more or less.
The TH sound has a relatively low functional load. Therefore, dey for they isn’t so bad an error.
However, a mix up between P and B has a higher functional load and can lead to more confusion if pit and bit are pronounced incorrectly.
Rang and Moran (2014) studied the differences in errors made across 4 levels of English language proficiency and the most significant improvement across levels was found mostly in the high functional load errors, but not necessarily in the low functional load errors.
By targeting high functional load differences, English language learners can get the biggest bang for their buck. Furthermore, it means non-native English communicators can still perform well and communicate effectively regardless of their complete conformity to native norms.