U.S. retail sales at discount, chain and department stores fell sharply during the five weeks ended October 6 as consumers guarded their wallets following the attacks on the United States, Instinet Research reported in its weekly Redbook Retail Sales Average on Tuesday.

The period covers two weeks before and three weeks after the Sept. 11 attacks.

The Redbook Retail Sales Average fell 2.5 percent during the five weeks compared with August, slightly worse than the 2.3 percent decline in the first four of those weeks, Redbook said.

On a year-over-year basis, the index fell 0.2 percent, the same rate of decline as reported in the preceding week.

"Many retailers were impacted by the tragic events that occurred on September 11, 2001, and the resulting effect on consumer confidence," Redbook said.

The Redbook Retail Sales Average is a sales-weighted average of annual growth in same-store sales at discount, department and chain stores that report their results on a weekly basis.

The average is compiled from a sample of general merchandise retailers representing about 9,000 stores. Same-store sales measure revenues at stores open at least a year.

The Redbook Average is released weekly by Instinet Research, a division of Instinet, a Reuters-owned electronic brokerage.