Good Afternoon Everyone, I am looking for advice fitting a linear mixed model where the random components do not seem to fit within the model formulae for lmer. The columns of Z are not stratified and have the notional random formula (z1 | 1) + ... + (zk | 1). Context I am fitting a penalised thin plate spline with knots k1 to kn. The basis functions Zk are |x-ki|^3 and the penalty matrix has elements |ki-kj|^3. Rather than fit basis functions Zk I have transformed the basis to Z = Zk %*% penalty^(-1/2). Full details are in section 2: Bayesian analysis for penalised spline regression using winBUGS. https://www.jstatsoft.org/article/view/v014i14/v14i14.pdf I am specifically looking for an alternative to the function spm() in package semipar. Thank you for any help or advice. Dave. David Mcnulty Medical Statistician Tel: +44 (0) 121 371 2448 Internal: 12448 Email: David.Mcnulty at uhb.nhs.uk Web: http://www.uhb.nhs.uk Health Informatics - University Hospitals Birmingham NHS Foundation Trust Yardley Court, 11-13 Frederick Road, Edgbaston Birmingham, B15 1JD The Health Informatics Department is a team of specialist NHS information analysts who work together to provide analysis solutions. The Team filters, analyses and presents comprehensive information that empowers NHS professionals to make informed decisions.