The San Diego Regional Chamber of Commerce’s measure of business optimism fell again in August to another year-long low, with larger firms showing the steepest drops in confidence.

The Chamber’s Business Outlook Index fell less than a point from 22.5 in July to 21.9. The index had fluctuated between 24 and 28 over the past year after falling to 18.5 last July when the city passed a minimum wage hike.

The Chamber said its monthly survey, which polled a random sample of 208 businesspeople, showed “staggeringly low” optimism from large firms, bringing down the overall index. They were much less confident about revenue, business conditions and the hours they would offer to their employees than small and mid-sized companies. One factor could be the stock market volatility from mid-August, which likely had greater impact on larger companies, according to the Chamber.

Manufacturers, however, had an extremely positive outlook, leading all other sectors with an index of 57.

The survey also asked respondents what share of CEO positions in their industries they believed were held by women. Only 37 percent of those executives are women, according to the respondents’ estimates.