Securities firms laid off nearly 16,000 people between the Oct. 19 stock market plunge and the end of March, according to a study released Wednesday.

The joint study by the Securities Industry Association and Arthur Andersen & Co., titled "Wall Street's Work Force," shows that 15,900 people lost their jobs in the five months after the market collapse - 6,900 brokers and 9,000 support staff members."Although the layoffs were painful in human terms, they were a necessary part of the industry's across-the-board efforts to lower expenses, which were rising out of control (and) causing diminishing profit margins and lower returns on investment," said Edward O'Brien, president of the Securities Industry Association.

Almost all of the dismissals occurred at national full-line brokerages and investment banks.