Chapter 27. Pooled Time Series, Cross-Section Data

826—Chapter 27. Pooled Time Series, Cross-Section Data

specific variable, you should have a separate series corresponding to each cross-section/ variable combination. For example, if you have time series data for an economic variable like investment that differs for each of 10 firms, you should have 10 separate investment series in the workfile with names that follow the user-defined convention.

Lastly, and most importantly, a pool workfile must contain one or more pool objects, each of which contains a (possibly different) description of the pooled structure of your workfile in the form of rules specifying the user-defined naming convention for your series.

There are various approaches that you may use to set up your pool workfile:

•First, you may simply create a new workfile in the usual manner, by describing, the time series structure of your data. Once you have a workfile with the desired structure, you may define a pool object, and use this object as a tool in creating the series of interest and importing data into the series.

•Second, you may create an EViews workfile containing your data in stacked form. Once you have your stacked data, you may use the built-in workfile reshaping tools to create a workfile containing the desired structure and series.

Both of these procedures require a bit more background on the nature of the pool object, and the way that your pooled data are held in the workfile. We begin with a brief description of the basic components of the pool object, and then return to a description of the task of setting up your workfile and data (“Setting up a Pool Workfile” on page 831).

The Pool Object

Before describing the pooled workfile in greater detail, we must first provide a brief description of the EViews pool object.

We begin by noting that the pool object serves two distinct roles. First, the pool contains a set of definitions that describe the structure of the pooled time series, cross-section data in your workfile. In this role, the pool object serves as a tool for managing and working with pooled data, much like the group object serves is used as a tool for working with sets of series. Second, the pool provides procedures for estimating econometric models using pooled data, and examining and working with the results from this estimation. In this role, the pool object is analogous to an equation object that is used to estimate econometric specifications.

In this section, we focus on the definitions that serve as the foundation for the pool object and simple tools for managing your pool object. The tools for working with data are described in “Working with Pooled Data” beginning on page 838, and the role of the pool object in estimation is the focus of “Pooled Estimation” beginning on page 845.

828—Chapter 27. Pooled Time Series, Cross-Section Data

defines a different set of identifiers, and may be used to work with different sets of series in the workfile. Alternatively, you may have multiple pool objects in a workfile, each of which contain the same list of identifiers. A POOL04 that contains the same identifiers as POOL01 may be used to work with data from the same set of countries.

Second, since pool objects contain only definitions and not series data, deleting a pool will not delete underlying series data. You may, however, use a pool object to delete, create, and manipulate underlying series data.

Group Definitions

In addition to the main list of cross-section identifiers, you may define groups made up of subsets of your identifiers. To define a group of identifiers, you should enter the keyword “@GROUP” followed by a name for the group, and the subset of the pool identifiers that are to be used in the group. EViews will define a group using the specified name and any identifiers provided.

We may, for example, define the ASIA group containing the “_JPN” and “_KOR” identifiers, or the NORTHAMERICA group containing the “_USA” identifier by adding:

@group asia _jpn _kor

@group northamerica _usa

to the pool definition.

These subsets of cross-section identifiers may be used to define virtual series indicating whether a given observation corresponds to a given subgroup or not. The ASIA group, for example, can be used along with special tools to identify whether a given observation should be viewed as coming from Japan or Korea, or from one of the other countries in the pool. We describe this functionality in greater detail in “Pool Series” on page 830.

Viewing or Editing Definitions

You may, at any time, change the view of an existing pool object to examine the current list of cross-section identifiers and group definitions. Simply push the Define button on the toolbar, or select View/Cross-Section Identifiers. If desired, you can edit the list of identifiers or group definitions.

Copying a Pool Object

Typically, you will work with more than one pool object. Multiple pools are used to define various subsamples of cross-section identifiers, or to work with different pooled estimation specifications.

To copy a pool object, open the original pool, and select Object/Copy Object… Alternatively, you can highlight the name of the pool in the workfile window, select Object/Copy Selected… and enter the new name.