How much of your portfolio should be in stocks? It's one of investing's most important questions — and the standard answer is costing the average investor the equivalent of 2% of their lifetime consumption. Yale economists have finally built something better, and it fits in a spreadsheet.
S&P 500 concentration risk is at historic highs. If you own a global tracker, your portfolio may be far less diversified than you think. Here's what you can do about it.
