User Guide

168
Chapter 7
SPSS Command Syntax Reference for information on using the DATE command
to create cu
stom date variables.)
First Case Is. Defines the starting date value, which is assigned to the first case.
Sequential values, based on the time interval, are assigned to subsequent cases.
Periodicit
y at higher level.
Indicates the repetitive cyclical variation, such as the
number of months in a year or the number of days in a week. The value displayed
indicates the maximum value you can enter.
A new numeric variable is created for each component that is used to define the date.
The new var
iable names end with an underscore. A descriptive string variable, date_,
is also created from the components. For example, if you selected
Weeks, days, hours,
four new variables are created: week_, day_, hour_,anddate_.
If date var
iables have already been defined, they are replaced when you define new
date variables that will have the same names as the existing date variables.
To Define D
ates for Time Series Data
E From the m
enus choose:
Data
Define Dates...
E
Select a time interval from the Cases Are list.
E Enter the value(s) that define the starting date for First Case Is, which determines the
date assigned to the first case.
Date Vari
ables versus Date Format Variables
Date vari
ables created with Define Dates should not be confused with date format
variables, defined in the Variable view of the Data Editor. Date variables are used
to establish periodicity for time series data. Date format variables represent dates
and/or t
imes displayed in various date/time formats. Date variables are simple
integers representing the number of days, weeks, hours, etc., from a user-specified
starting point. Internally, most date format variables are stored as the number of
seconds
from October 14, 1582.