De Boeck P, Bakker M, Zwitser R, Nivard M, Hofman A, Tuerlinckx F, Partchev I. The Estimation of Item Response Models with the lmer Function from the lme4 Package in R. J. Stat. Soft. [Internet]. 2011 Mar. 9 [cited 2024 Apr. 20];39(12):1-28. Available from: https://www.jstatsoft.org/index.php/jss/article/view/v039i12