An investigation into questionable circulation figures for US publications has cast its net further.

The Securities and Exchange Commission has requested documents from, among others, Dow Jones, Knight Ridder, the New York Times Company and the Washington Post Company.

The inquiry was set after Tribune-owned Newsday and Hoy, the Hollinger International-owned Chicago Sun-Times, and the Belo Corporation's Dallas Morning News admitted to exaggerating sales by tens of thousands of copies daily.

As a result, investors and advertisers alike have lost confidence in circulation figures across the board. The data is also used as a guide to the financial stock of newspaper companies and to regulate the cost of page rates.

The SEC letters to other newspaper companies are, say sources close to the Commission, not an indication of wrongdoing but an attempt to find out whether irregularities are commonplace, or whether those uncovered were isolated incidents – which might allow the scandal to quieten down.

Among the less upstanding practices uncovered were the delivery of newspapers free to homes while claiming they were genuine sales and inducing distributors not to return unsold copies.

Data sourced from New York Times; additional content by WARC staff