Difference between N/A (not applicable) and missing observations


I was facing a question regarding the difference between observations that are “not applicable” and observations that are missing. I would be thankful for any help on this.

Observations that are “Not Applicable (N/A)” are “Not In Universe (NIU)” for a specific variable, meaning that the question was not asked of that particular person or household. Missing observations are in-universe cases in which a response was not recorded (that should have been, according to the universe description of that variable) for various reasons, such as: the respondent was temporarily absent, the respondent refused to answer a question, or no one was home. For example, people who have lived in the United States for less than one year are assigned an “N/A” code of “0” for the variable YRSUSA2 (Years in the United States, Intervalled), whereas people who do not answer the question are assigned a “Missing” code of “9”.

Thank you for the clear explanation!