About US User Datasets

Forecast Period versus Prediction Period
We will use the phrase "forecast period" to refer to the actual forecast period in the base dataset, currently 2001:4-2005:4. You may, however, deal with any period within the overall 1952:1-2005:4 period, and we will use the phrase "prediction period" to refer to the period you have chosen. The only restriction is that if you are going to solve the model, the prediction period cannot begin earlier than 1954:1.

The US Model Datasets
Everything about the model is stored in a single dataset:

  1. values on all the endogenous and exogenous variables from 1952:1 through 2005:4,
  2. specification information, and
  3. coefficient estimates.
The dataset for the November 1, 2001, update of the model is called BASE with a password of BASE. You will name and create your own dataset, using BASE as a starting point. Say you call your dataset NEW and give it the password of NEW. When you first start, NEW and BASE are exactly the same, and then NEW gets modified as you make changes (change exogenous variables, coefficients, etc.). Once you are done making changes, you tell the program to solve the model. The program solves the model, and after this solution, the values of the endogenous variables in NEW are the predicted values. You can examine (i.e., write to the screen, print to a printer, or download to a file) the values in BASE and in any datasets you create.

In many cases one is interested in how the values of the endogenous variables in NEW compare to the original values in BASE. Say that you changed federal government purchases of goods (COG) for the forecast period and are interested in how this change affected real GDP (GDPR). You can simply tell the program that you want to compare GDPR in NEW versus BASE, and it will show you the two sets of values and the differences. (Once you do this a few times you will get the hang of it.)
WARNING: A comparison done this way only works if you take the beginning of your prediction period to be no earlier than the beginning of the forecast period in BASE. See Section 2.6 in Chapter 2 of The US Model Workbook for what needs to be done for comparisons within a period for which historical data exist. This is important: Do not take your prediction period to begin earlier than the forecast period until you have read Section 2.6.

The program is flexible as to what you take as your base dataset. Although the first time you start the base dataset is BASE, after you have created new ones, you can use any of these as your base. For example, if you created NEW and now want to makes further changes and create NEW1, you simply tell the program that you want NEW as your base dataset. Once you have created NEW1, you can either compare the values in NEW1 with those in NEW or the values in NEW1 with those in BASE. You do this by simply telling the program which two datasets to use for the comparison.

If you make changes to your dataset and do not ask the program to solve it (which you are allowed to do), the values of the endogenous variables in the dataset are not consistent with your changes because they are not the solution values. Make sure you remember whether your dataset has been solved. As a general rule, you might always solve your datasets immediately after you have made your changes.

Units of the Variables
Although the flow variables in the US model are at quarterly rates, for most purposes it is useful to work with variables at annual rates. For the most part you will work with variables at annual rates: the program lists the variables at annual rates and your changes are taken to be at annual rates. The only time you need care about quarterly rates is if you are downloading the data to your computer for estimation purposes, since for estimation purposes the variables should be at quarterly rates. There is an option in the program to download the data at quarterly rates.

Notation for Quarters
When you type a quarter, such as the fourth quarter of 1996, you type 19964. In the documentation, however, the notation 1996:4 is sometimes used. You should not type the colon when entering the quarter you want.

Solution Errors
If you make wild changes to the exogenous variables or coefficients, the model may not solve. When the model does not solve, you will get a solution error message, and the existing values of the endogenous variables in your dataset will not be changed. (Your dataset will still be inconsistent in the sense discussed above.) You need to be less wild and try again. As a general rule, as discussed in Chapter 2 of The US Model Workbook, you should not try to push the economy into extreme areas. Macroeconometric models are not likely to be reliable when variable values are pushed far beyond their historical ranges.

Notation for the Variables
If you are going to work with the US model, it may be useful to print Appendix A and the Chapter 5 tables for ease of reference. The notation in the software matches the notation in Appendix A almost exactly. One exception concerns the option to "Modify the equations." If you are unclear about the left and right hand side variables, consult Appendix A and the Chapter 5 tables. The notation is fairly clear in the software except for equations 19 and 29, where the notation for the left and right hand side variables is stupid.

You should also note that equation 12, which explains the capital stock of the firm sector (KK), is sometimes referred to in the software as the IKF equation. Equation 12 used to explain IKF, but it now explains KK, with IKF being determined by identity 92.