@article {pmid22241689, title = {Mixed effect Poisson log-linear models for clinical and epidemiological sleep hypnogram data}, journal = {Stat Med}, volume = {31}, number = {9}, year = {2012}, month = {Apr}, pages = {855{\textendash}870}, author = {Swihart, B and Caffo, B and Crainiceanu, C and Punjabi, N.M.} }