7.6 Missing values carry information

NA, blank, zero, Unknown, Not asked, and Not applicable may describe different processes. Combining them without investigation can hide a system problem or change the population being analyzed.

For each variable, determine:

• how missing information is stored;
• whether different missing states have different meanings;
• whether missingness is expected under a business rule;
• whether the pattern changes by time, source, location, or group; and
• whether the missing value prevents a valid calculation.

If no values are missing, record a count of zero for the current version. This confirms that the field was checked.