A stock index that captures the top 20% of the largest 600 companies in the Dow Jones Global Index that are based in North America. Companies are evaluated based on both general and industry-specific sustainability trends by Zurich-based SAM Group, a research firm that surveys thousands of global blue-chip companies each year. The free-float market capitalization weighted index is reviewed quarterly for share count changes, and reconstituted annually once updated surveys have been completed for all potential index members. Each company in the 600 stock universe is given a sustainability score based on progress in areas such as corporate governance, climate change strategy and energy consumption as well as industry-specific variables. Taobiz explains Dow Jones Sustainability North America Index Much of what are considered positive strategies for long-term economic and social responsibility don't have the short-term payoffs that shareholders are used to seeing, such as lower operating costs or higher revenues. The benefits to a company for focusing on sustainability could take many years to be realized, so short-term financial performance may not be indicative of long-run savings or shareholder approval. In addition to the main index, there are specialized sub-indexes that have filtered out industries such as alcohol, tobacco, firearms, and gambling. The North American index was first created in September 2005.