One of my friends asked me how MSCI World performed against the S&P 500 in the past. He was deciding whether there is a solid reason to own a global large-cap and mid-cap index rather than a pure US index ETF. MSCI only has the data for various developed worlds starting from 1970, so we can only compare the performance for the past 52.5 years. We can compare the performance by taking the returns of the S&P 500 index minus the returns of the MSCI World index. If the returns are positive, the S&P 500 outperforms the MSCI World. If the returns are negative, the S&P 500 underperforms the MSCI World. Since the US forms between 40% and more of the MSCI World at various past junctures, we can see how different the international developed stocks (does not include emerging markets) perform against the US. How the S&P 500 did over one year versus the MSCI World if we roll month by month:...