If categories of serious events are collected secondarily to a leading question, as in the example below, the values of the variables that capture reasons an event is considered serious (i.e., AESCAN, AESCONG, etc.) may be null.
For example, if Serious is answered “No,” the values for these variables may be null.
However, if Serious is answered “Yes,” at least one of them will have a “Y” response. Others must be blank (BHC-example 1).