I’m working with the ACS 2009-2011 IPUMS data. In the occupational 2002 recode (occp02), two-thirds of respondents are classified as “N.A.” It’s about one-third in the 2010 recode (occp10). The data dictionary defines N.A. as “Code classification is Not Applicable, record in universe.” These people are in the universe, because missing values are used for those who are “less than 16 years old/NILF who last worked more than 5 years ago or never worked”.
What does “Code classification is Not Applicable” mean? Am I being dense? Does it mean that the coders were unable to classify the worker? It would be surprising for that to happen to so many respondents.