The contribution of research and development to a company's market value has grown considerably in recent years. In the mid-1970s, accountants were able to capture on their ledgers 90-95% of a firm's book value, but by 2000 the importance of intangible assets had grown to the point where they could account for only 13-15%. Financial economists and accountants have investigated the link between a firm's market value and its R&D spending, and various factions advocate a variety of positions on the amount and rate of investment, investors' ability to capture returns on that investment, and ways to measure value, investment, and returns.