The AHS National sample is longitudinal from 1985 to 2013, then again from 2015 moving forward.  Though the survey visits the same housing units each cycle, units may be removed or added for various reasons throughout the survey process. The intent of the Sample Case History Files (also known as the “Where Did They Go” files) is to track all cases that were interviewed in each longitudinal panel and provide basic information on the interview status.  The 2015 to 2023 file includes National and Metropolitan cases.