A missing or missing value is a value in a Variable which represents a reason why no observation (ValidResponse) has been stored. It also contains its frequency.
The absolute number of occurrences of this missing. Must not be empty.
A (unique in this Variable) code for this missing. Must not be empty.
A label describing this missing. Must not contain more than 512 characters.
The quotient from absoluteFrequency and Distribution.totalAbsoluteFrequency. Must not be empty.