Define Dates
The Define Dates dialog box allows you to generate date variables that can be used to establish the periodicity of a time series and to label output from time series analysis.
Cases Are. Defines the time interval used to generate dates.
- Not dated removes any previously defined date variables. Any variables with the following names are deleted: year_, quarter_, month_, week_, day_, hour_, minute_, second_, and date_.
- Custom indicates the presence of custom date variables created with command syntax (for example, a four-day workweek). This item merely reflects the current state of the active dataset. Selecting it from the list has no effect. (For information on creating custom date variables, see the DATE command.)
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.
Periodicity 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. For hours, minutes, and seconds the maximum is the displayed value minus one.
A new numeric variable is created for each component that is used to define the date. The new variable 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_, and date_.
If date variables 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 Dates for Time Series Data
- From the menus choose:
- Select a time interval from the Cases Are list.
- Enter the value(s) that define the starting date for First Case Is, which determines the date assigned to the first case.