The Joint Committee on Taxation has issued Overview Of Revenue Estimating Procedures And Methodologies Used By The Staff Of The Joint Committee On Taxation (JCX-1-05).  Here is a portion of the Executive Summary:

This document provides an overview of the current procedures used in the revenue estimating process. The emphasis is solely on methodology and issues associated with the preparation of conventional revenue estimates of proposed changes to the Internal Revenue Code. The report provides a summary of the revenue estimating responsibilities of the Joint Committee staff; discusses requirements, constraints, and conventions of the revenue estimating process; and presents the estimating procedures and models used by the Joint Committee staff in preparing revenue estimates. This summary provides a brief discussion of the principal topics covered in the report:

• Overview of Revenue Estimating Responsibilities
• Background on Revenue Estimating and Budget Act Requirements
• The Budget Window and Presentation of Estimates
• Behavioral Effects in Revenue Estimates
• Compliance, Administration and Enforcement Costs
• Indirect Tax Effects
• Distributional Analysis
• Tax Models