What is the Mixed - Models Controversy ? From :

Two papers have recently been published in this journal which purport to deal with the mixedmodels controversy (Lencina et al., 2005; Lencina & Singer, 2006, to be referred to as L1 and L2). In my view they do not represent the current state of thinking on this subject. My own work begins with Nelder (1977) and continues with papers in 1982, and particularly with Nelder (1994, 1995). Further papers are Nelder (1997), whose title includes the phrase ‘The great mixed-model muddle’, and Nelder (1998). In Nelder (1994) I describe what I regard as three false steps that have generated confusion and show how a consistent treatment may be developed. The two most important ideas are (1) marginality relations between terms in a factorial model, and (2) why constraints must not be put on parameters because they are required on estimates.