Lexicostatistics is an approach to comparative linguistics that involves quantitative comparison of lexical cognates. Lexicostatistics is related to the comparative method but does not reconstruct a proto-language. It is to be distinguished from glottochronology, which attempts to use lexicostatistical methods to estimate the length of time since two or more languages diverged from a common earlier proto-language. This is merely one application of lexicostatistics, however; other applications of it may not share the assumption of a constant rate of change for basic lexical items.
The term "lexicostatistics" is misleading in that mathematical equations are used but not statistics. Other features of a language may be used other than the lexicon, though this is not usual. Whereas the comparative method used shared identified innovations to determine sub-groups, lexicostatistics does not identify these. The latter is a distance based method but the comparative method considers language characters directly. The lexicostatistics method is a simple and fast technique relative to the comparative method but has limitations that are discussed below. It can be validated by cross-checking the trees produced by both methods.
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Lexicostatistics was developed by Morris Swadesh in a series of articles in the 1950s, based on earlier ideas. The concept's first known use was by Dumont d'Urville in 1834 who compared various "Oceanic" languages and proposed a method for calculating a coefficient of relationship. Hymes (1960) and Embleton (1986) both review the history of lexicostatistics.
The aim is to generate a list of universally used meanings (hand, mouth, sky, I). Words are then collected for these meaning slots for each language being considered. Swadesh reduced a larger set of meanings down to 200 originally. He later found that it was necessary to reduce it further but that he could include some meanings that were not in his original list, giving his later 100-item list. The Swadesh List in Wiktionary gives the total 207 meanings in a number of languages. Alternative lists for particular purposes have been generated e.g. Dyen, Kruskal and Black have 200 meanings for 84 Indo-European languages in digital form.
A trained and experienced linguist is needed to make cognancy decisions. However, the decisions may need to be refined as the state of knowledge increases. However, lexicostatistics does not rely on all the decisions being correct. For each pair of lists the cognacy of a form could be positive, negative or indeterminate. Sometimes a language has two words for one meaning, e.g. small and little for not big.
This percentage is related to the proportion of meanings for a particular language pair that are cognate, i.e. relative to the total without indeterminacy. This value is entered into a N x N table of distances, where N is the number of languages being compared. When complete this table is half-filled in triangular form. The higher the proportion of cognacy the closer the languages are related.
Creation of the language tree is based solely on the table found above. Various sub-grouping methods can be used but that adopted by Dyen, Krustal and Black was:
Calculations have to be of nucleus and group lexical percentages.
A leading exponent of lexicostatistics application has been Isidore Dyen. He used lexicostatistics to classify Austronesian languages as well as Indo-European ones. A major study of the latter was reported by Dyen, Kruskal and Black (1992). Studies have also been carried out of Amerindian and African languages.
People such as Hoijer (1956) have showed that there were difficulties in finding equivalents to the meaning items while many have found it necessary to modify Swadesh's lists. Gudschinsky (1956) questioned whether it was possible to obtain a universal list.
Factors such as borrowing, tradition and taboo can skew the results, as with other methods. Sometimes lexicostatistics has been used with lexical similarity being used rather than cognacy to find resemblances. This is then equivalent to mass comparison.
The choice of meaning slots is subjective as is the choice of synonyms.
Some of the modern computational statistical hypothesis testing methods can be regarded as improvements of lexicostatistics in that they use similar word lists and distance measures.