The strongest brands held up best during the down market of April 13-18, brand strategy firm Corporate Branding L.L.C. said in a report released Friday. It showed that share prices of tier-one brands declined an average of 0.8%, while the weakest brands plummeted 3.2%. Corporate Branding, Stamford, Conn., said the study demonstrates the financial benefits of effective brand management. The company breaks brands into five separate categories through a power ranking, created by interviewing top executives at the top 20% of U.S. companies, measured by revenue. Examples of top brands would be Coca-Cola, General Electric and Walt Disney Co., while bottom-rated brands include Kellwood Co., Valero Energy and System Software.