Log-likelihood and odds ratio: Keyness statistics for different purposes of keyword analysis

TLDR

Keyword analysis is used across applied linguistics sub‑disciplines, from genre studies to critically‑oriented research, to characterize genres or identify text‑specific ideological issues. This study compares log‑likelihood (LL) and odds ratio (OR) for keyword identification, arguing that the two methods yield different keywords suited to distinct research purposes. The authors conduct two case studies—keyword analyses of advance fee scams versus the British National Corpus and applied linguistics articles versus other disciplines—to compare LL and OR outputs. LL highlights relatively common words serving genre purposes, whereas OR highlights more specialized words serving critically‑oriented purposes, and the study discusses methodological and practical contributions to keyword analysis.

Abstract

Abstract Keyword analysis is used in a range of sub-disciplines of applied linguistics from genre analyses to critically-oriented studies for different purposes ranging from producing a general characterization of a genre to identifying text-specific ideological issues. This study compares the use of log-likelihood (LL), a probability statistic, and odds ratio (OR), an effect size statistic, for keyword identification and argues that the two methods produce different keywords applicable to research focusing on different purposes. Through two case studies, keyword analyses of advance fee scams against the British National Corpus and research articles in applied linguistics against research articles from other academic disciplines, we show that both the LL and OR keywords concern the aboutness of the corpus, but differ in their specificity and pervasiveness through the corpus. LL highlights words which are relatively common in general use serving genre purposes, whereas OR highlights more specialized words serving critically-oriented purposes. Methodological and practical contributions to keyword analysis are discussed.