Stocks resumed their push to record highs, regaining ground lost amid a choppy start to the year. The Morningstar US Market Index rose 1.7% in the past week and is up roughly 27% over the past year.

There are many ways to diversify beyond the S&P 500. One is to hold shares of the Invesco S&P 500 Equal Weight ETF RSP. Another, according to Davis, is to take an even broader index-fund approach. One ...