In an article in the American Psychologist there is a series of bar graphs with a statistic next each bar. The statistic is described in the text and in the graph captions as being an effect-size measure. The statistics is $\lambda^2$. Now, I can find explanations of $\eta^2$, Wilks $\lambda$, and Cohen's $f^2$ as effect size measures but not of $\lambda^2$. What have I missed? Or is it more likely a typograpical error of some kind?