The most thorough way to decide on similarities between words on different word lists is through the use of the Comparative Method to establish which word pairs are cognate. In this case, if words are cognate, then they are considered to be lexically similar and the lexical similarity percentage can also be called a cognate percentage. However, as Frank Blair says in his 1990 book Survey on a Shoestring<ref name="blair">Blair, Frank. 1990. Survey on a Shoestring. Dallas: SIL.</ref>, “this process is often more time-consuming than a researcher on survey could desire. It also may require information not readily available to the surveyor.”
If the only use for the word list is to screen for low intelligibility, the Comparative Method may be too time-consuming and, as this method favours large lists of words, there may not be enough data from an intelligibility survey to apply it anyway. Surveyors should keep this end in mind when deciding how many words to collect. Collecting more data than you require will not only meet your needs adequately but can also better serve the greater linguistic community by enabling other types of analysis to be applied.