The goal of the study was to figure out how big a diversified investment portfolio needs to be. The researchers used two methods to answer this question. They found that as a portfolio gets bigger, the risk of returns changing over time levels off, but the risk of returns varying between portfolios of the same size keeps increasing. By comparing different portfolios to a benchmark, they determined that a well-diversified portfolio should have at least 30 investments. This number could be higher depending on factors like how long you plan to invest and the costs involved. The study also showed that randomly selecting investments doesn't necessarily lead to a smaller, more diversified portfolio.