Data analytics conducted by Dow Jones Market Data shows that the rolling correlation between gold and the S & P 500 has been 0 since 1975, which means there is no linear relationship (1 represents a perfect positive correlation). Since November 2014, the correlation between bitcoin and the S & P 500 has been 0.21, while the correlation between bitcoin and gold has been 0.09. George Milling-Stanley, chief gold strategist at State Street Global Advisors, said that bitcoin's returns over its still-short lifespan cannot be ignored either, but investors should be aware that they also add a lot of risk to their portfolios in their search for returns, given that bitcoin has been more volatile than gold over the past 15 years.