Final answer:
In SAS, the default length for numeric variables is 8 bytes, which would apply to the Birth_Date column unless otherwise specified.
Step-by-step explanation:
The question references the output of the PROC CONTENTS procedure in SAS, which is used to display metadata about variables in a SAS dataset. The default length of the Birth_Date column, as shown in the output snippet, is not explicitly mentioned
However, in SAS, the default length for numeric variables, which is the type of the Birth_Date column, is 8 bytes. Therefore, unless specified otherwise in the dataset or altered by the user, the default length of the Birth_Date column should be expected to be 8 bytes.