Not all funds that track the same index are created equal. For some, inequality is part of the design. Take the S&P 500 and the S&P 500 SPDR E.T.F.

Apple is the S&P 500’s largest constituent, 4.7 percent in early January. News Corporation, the smallest member, accounted for less than 0.01 percent of the index.

That’s because the S&P 500, like many other major indexes, are “capitalization weighted,” meaning that each company’s value, or market capitalization, determines how much weight it has in the index. The idea is to get a faithful representation of the stock market by giving each individual stock its appropriate relative value.

But that’s not the only way to build an index.

One alternative is to maintain roughly the same allocation to every company. An equal-weighted version of the S&P 500, for example, will adjust its holdings periodically to ensure that Apple, News Corporation and everything in between makes up just 0.2 percent of the portfolio. The Invesco S&P 500 Equal Weight E.T.F. does that.