Using gret l for Principles of Econometrics, 4th Edition

Importing Data

Obtaining data in econometrics and getting it into a format that can be used by your software can be challenging. There are dozens of different pieces of software and many use proprietary data formats that make transferring data between applications difficult. You’ll notice that the authors of your book have provided data in several formats for your convenience. In this chapter, we will explore some of the data handling features of gretl and show you (1) how to access the data sets that accompany your textbook (2) how to bring one of those data sets into gretl (3) how to list the variables in the data set and (4) how to modify and save your data. Gretl offers great functionality in this regard. Through gretl you have access to a very large number of high quality data sets from other textbooks as well as from sources in industry and government. Furthermore, once opened in gretl these data sets can be exported to a number of other software formats.

First, we will load the food expenditure data used in chapter 2 of POE4. The data set contains two variables named x and y. The variable y is weekly expenditures on food in a household and x is weekly income measured in $100 increments.

Open the main gretl window and click on File>Open data>Sample file as shown in Figure 1.4.

Alternately, you could click on the open dataset button on the toolbar. The button looks like a folder and is on the far right-hand side of the toolbar. This will open another window (Figure 1.5) that contains tabs for each of the data compilations that you have installed in the gretl/data

directory of your program. If you installed the data sets that accompany this book using the self extracting windows program then a tab will appear like the one shown in Figure 1.5.

it using the cursor, and open it using the ‘open’ button bring the variables of the food expenditure data set into gretl. At this point, select Data on the menu bar and then Display values as shown in Figure 1.6.

From the this pull-down menu a lot can be accomplished. You can edit, add observations, and impose a structure of your dataset. The structure of your dataset is important. You can choose between time-series, cross sections, or panel data structures. The options Gretl gives you depend
on this structure. For instance, if your data are structured as a time-series, gretl will allow you to take lags and differences of the variables. Certain procedures that can be used for time-series analysis will only be available to you if your dataset has been structured structured for it. If a gretl command is not available from the defined dataset structure, then it will be greyed out in the pull-down menus.

Notice in Figure 1.4 that gretl gives you the opportunity to import data. Expanding this (File>Open data>Import) gives you access to several other formats, including Stata, Excel, Eviews, SPSS, and SAS (if installed). For instance, simply dragging a Stata dataset onto the main gretl window will bring the data into gretl.

Also, from the File pull-down menu you can export a data set to another format. The export feature is particularly useful for getting data into R.

If you click on File>Databases>On database server (Figure 1.4) you will be taken to a web site (provided your computer is connected to the internet) that contains a number of high quality data sets. You can pull any of these data sets into gretl in the same manner as that described above for the POE4 data sets. If you are required to write a term paper in one of your classes, these data sets may provide you with all the data that you need. The database server is discussed in more detail below.