Internet research firm The Yankee Group laid off about 13 percent of its 200-plus staff on Monday, said sources within the company. About 41 workers were laid off, and many of the cuts included analysts who help cover e-commerce. Yankee Group executives held meetings Monday with most of the staff to discuss the layoffs. The struggling e-commerce sector has prompted several analyst groups to reorganize their coverage and de-emphasize e-commerce groups. In January, Jupiter Media Metrix, which tracks visits to Web sites and analyzes Internet use, cut 80 jobs, or about 8 percent of its work force.