This paper analyzes underreporting and under-presentation of high expenditure cases in the Medical Expenditure Panel Survey (MEPS).  The study finds that underreporting effected all groups but uniformly so that behavioral analyses were unaffected.  

Zuvekas, S. H. and G. L. Olin (2009). Accuracy of Medicare expenditures in the medical expenditure panel survey. Inquiry, 46(1): 92-108.  http://www.ncbi.nlm.nih.gov/pubmed/19489486 

Authors: Samuel H. Zuvekas, Gary L. Olin