Occasionally, sample size limitations make it necessary to pool two or more years of MEPS expenditure data to produce expenditure estimates of acceptable precision (for example, to analyze infrequently occurring health conditions or small demographic subpopulations). For a detailed explanation of how to pool two or more years of MEPS data, please refer to documentation for the pooled linkage variance estimation data file:
https://meps.ahrq.gov/data_stats/download_data/pufs/h036/h36u20doc.pdf.