of passive investing. John C. Bogle of The Vanguard Group, while a staunch advocate for passive investing overall, also argued in 2018 that the growth in passive management firms would soon result in a concentration of over half of American stock ownership, and associated proxy voting power, among three large firms (Vanguard, State Street Global Advisors and BlackRock). Bogle stated: "I do not believe such a concentration would serve the national interest". In 2017, Robert Shiller, a Nobel Prize winning economist at Yale University, stated passive index funds are a "chaotic system" and "kind of pseudoscience" due to what he described as an over-reliance on computer models and a neglect of the businesses whose stocks make up index funds. According to researchers with the Federal Reserve who published their findings in 2020, the growing popularity of passive investing has increased some risks for investors and the economy generally, but reduced other risks. "Some passive strategies amplify market volatility, and the shift [towards passive investing] has increased industry concentration, but it has diminished some liquidity and redemption risks." Passive investing may contribute to shareholder apathy, whereby investors are less engaged in the corporate governance process. In response, defenders of passive investing argue that some claims against the strategy are incorrect, and that other claims are partially accurate but overstated. Implementation The first step to implementing an index-based passive investment strategy is choosing a rules-based, transparent, and investable index consistent with the investment strategy's desired market exposure. Investment strategies are defined by their objectives and constraints, which are stated in their Investment Policy Statements. For equity passive investment strategies, the desired market exposures could vary by equity market segment (broad market vs. industry sectors, domestic vs. international), by style (value, growth, blend/core), or by other factors (high or low momentum, low volatility, quality). Index rules could include the frequency at which index constituents are re-balanced, and criteria for including such constituents. These rules should be objective, consistent and predictable. Index transparency means that index constituents and rules are clearly disclosed, which ensures that investors can replicate the index. Index investability means that the index performance can be reasonably replicated by investing in the market. In the simplest case, investability means that all constituents of an index can be purchased on a public exchange. Once an index has been chosen, an index fund can be implemented through various methods, financial instruments, and combinations