Deciding on the unit of counting for developing word lists
The role and value of word list research for ESP
The unit of counting is an important aspect of word list development. Units of counting can include individual word types, lemmas or word families. Types are individual words. For example, dog and dogs are both types. An advantage of counting types for ESP word lists is that individual types may be technical words, whereas items in a word family might include items that are technical vocabulary as well as items which are not technical in nature. For example, patient might be a technical word in Nursing, but patience is not. A lemma contains the inflected forms of a word, for example, like, likes, likes and liking. The unit of counting selected for a word list depends on the purpose of the word list.
A word family is a much broader unit of counting than individual types and lemmas. It contains the inflections and derivative forms of a word. Bauer and Nation (1993) categorise affixation in English and provide a series of levels of affixation. For example, the AWL was developed up to Level Six of Bauer and Nation’s (1993) scale. Here is an example of a word family from the AWL: benefit, beneficial, beneficiary, beneficiaries, benefited, benefiting and benefits. Nation and Webb (2011) point out that the decision on the unit of counting depends on the purpose of the word list.
If a word list is being used to measure the vocabulary load of written texts, then a word family is perhaps the most useful unit of counting. In each case of specialised word lists, for example in Carpentry or Aviation, then word types might be the better unit, because individual types might be classified as technical or specialised vocabulary, as the example of file mentioned earlier. Output from computer programmes such as RANGE (Heatley, Nation & Coxhead, 2002) reports on both type and family frequency and range, which means that types can be considered for selection in ESP word lists relatively easily. Nation (2016) has more definitions and examples of types, lemmas and word families, pointing out that lemmas are really one kind of word family.