EXHIBIT 16.1 [ANDERSON LOGO] April 5, 2002 ARTHUR ANDERSEN LLP Office of the Chief Accountant 225 Franklin Street Securities and Exchange Commission Boston MA 02110-2812 450 Fifth Street, N.W. Washington, D.C. 20549 Tel 617 330 4000 Fax 617 453 0731 Dear Sir/Madam: We have read paragraphs two and three of Item 4 included in the Form 8-K dated April 5, 2002 of Forrester Research, Inc. filed with the Securities and Exchange Commission and are in agreement with the statements. Very truly yours, /s/ Arthur Andersen LLP - ------------------------------- Arthur Andersen cc: Mr. Warren Hadley, CFO Forrester Research, Inc.