Missing values

The missing value marker is -999 by default, although this may be changed to another number by using the missing  control. This value is used to announce undefined cases to [B/D]; it is used with all three kinds of data definition: reading in multiple data cases as in §8.2, defining single observations as in §8.3, and the construction of data over many cases as in §8.4.

Any data value encountered which is equal to -999 (or the current missing value defined by the missing  control to replace the default value of -999) represents an undefined case. [B/D] does not store the missing value, it simple records it as missing. Thus, the appearance of -999 in data lists output by [B/D] probably indicates a bug in [B/D].

[B/D] never stores more data values than it needs to, and does not retain data-elements whose data consists entirely of missing values. Thus, it is quite possible for data-elements to be deleted by assigning missing values to them. Here is an example. Suppose that we introduce the data-element called with one observation, and then replace this observation by the missing value marker:

BD>data : d(1)=5.8

BD>data : d(1)=-999

This results in the deletion of the data-element d as finally it has no valid cases.