EViews Help: Panel Workfile Functions

Additional information is available in panel structured workfiles. EViews provides workfile functions that provide information about the cross-section, cell, and observation IDs associated with each observation in a panel workfile:

• @crossid: returns the cross-section index (cross-section number) of each observation.

• @cellid: returns the inner dimension index value for each observation. The index numbers identify the unique values of the inner dimension observed across all cross-sections. Thus, if the first cross-section has annual observations for 1990, 1992, 1994, and 1995, and the second cross-section has observations for 1990, 1995, and 1997, the corresponding @cellid values will be (1, 2, 3, 4) and (1, 4, 5), respectively.

• @obsid: returns the observation number within each panel cross section for each observation. @obsid is similar to @obsnum except that it resets to one whenever it crosses the seam between two adjacent cross sections.

Central to the notion of a panel trend is the notion that the trend values are initialized at the start of a cross-section, increase for successive observations in the specific cross-section, and are reset at the start of the next-cross section.

Beyond that, there are several notions of a time trend that may be employed. EViews provides four different functions that may be used to create a trend series: @obsid, @trendc, @cellid, and @trend.

The @obsid function may be used to obtain the simplest notion of a trend in which the values for each cross-section begin at one and increase by one for successive observations in the cross-section. To begin your trends at zero, simply use the expression “@OBSID-1”. Note that such a trend does not use information about the cell ID values in determining the value increment.

The calendar trend function, @trendc, computes trends in which values for observations with the earliest observed date are normalized to zero, and successive observations are incremented based on the calendar for the workfile frequency.

• @cellid, which returns an index into the unique values of the cell ID, returns a form of time trend in which the values increase based on the number of cell ID values between successive observations.

• @trend function is equivalent to “@cellid-1”.

In fully balanced workfiles (workfiles with the same set of cell identifier in each cross-section), the expressions “@obsid-1”, “@cellid-1”, and “@trend” all return the same values. Additionally, if the workfile follows a regular frequency, then the @trendc function returns the same values as @trend.

Note that because of the way they employ information computed across cross-sections, @trend and @trendc may not take the optional base_date argument in panel structured workfiles (see “Trend Functions”).