Why didn't you use Word Families?
For the NAWL, we followed the same criteria as for the NGSL. When West created the GSL, he combined the frequencies for the word regardless of part of speech, but he he did not include frequency counts for derived forms with the headword counts. For example, the frequency count for both the noun and verb forms of CARE are summed, while the frequency counts for the derived forms CAREFUL and CARELESS are listed separately.
Following the publication of Bauer and Nation’s Word Families (1993), the number of words forms included under the headword expanded greatly. They definition of “a word family consists of a base word and all its derived and inflected forms that can be understood by a learner without having to learn each form separately” (p. 253). For example, CARE under the word family rubric contains, along with the inflections of the verb and noun, the following, CARE, CAREFUL, CAREFULLY, CAREFULNESS, CARELESS, CARELESSLY, CARELESSNESS, CARER, CARERS, UNCARED, and UNCARING. However, the assumption that the form “can be understood by a learner without having to learn each form separately” has been called into question. Research by Schmitt and Zimmerman (2002) “did not support a strong facilitative effect for knowledge of words within a word family” (p. 158). Another problem with determining which words would be included under the headwords using the operationalization of the Word Family concept was suggested by Gardner (2007) who wrote “case by case assessments of affixed word forms would be necessary to determine if a prolific derivational affix was acting transparently or not” (p. 247). This of course adds a level of subjectivity to the compilation of the word list and an avenue to list differentiation, resulting in difficulty in interpreting coverage statistics reported for a variant word list going under the same name, such as is the case with the current GSL coverage claims coming from substantially different word lists.
Gardner, D. (2007). Validating the Construct of Word in Applied Corpus-based Vocabulary Research: A Critical Survey. Applied Linguistics, 28(2), 241–265.
Schmitt, N., & Zimmerman, C. B. (2002). Derivative word forms: What do learners know? TESOL Quarterly, 36(2), 145–171.