The Nikkei 225 is a stock market index for the Tokyo Stock Exchange that tracks the performance of Japan's top 225 blue-chip companies. It uses a price-weighted average methodology and covers approximately 50% of the total market capitalization of the TSE. Some of the top components include Toyota, NTT Docomo, and Mitsubishi UFJ Financial Group. The index is reviewed annually and components may be added or removed based on liquidity and representation of the market. It has been influenced by global economic factors and periods of Japanese economic growth and decline over the decades.