The popularity of the Nasdaq 100 index, which tracks the 100 biggest non-financial stocks on the exchange, is indicative of just how many investors are performance chasers, contends an article in Barron’s. But the index contains “some pretty head-scratching flaws with how [it] is constructed,” Morningstar analyst Ryan Jackson told Barron’s.

While the largest ETF tracking the index is the Invesco QQQ with its $196 billion in assets, investors would do better to buy more standard growth index funds like the Vanguard Growth or iShares Core S&P Growth funds, Jackson advises. For sector-focused investors, he recommends the Technology Select Sector SPDR and Vanguard Information Technology funds. Investors shouldn’t be constrained to the Nasdaq’s 100 stocks that only trade on its exchange, Jackson told Barron’s. Rather, they should give themselves as much opportunity as they can—particularly because companies in the Nasdaq 100 pay fees for their listing, and those that don’t pay are excluded from the index. In other words, the index exists in order to boost awareness of the exchange, Jackson maintains.

That’s a characterization that Jennifer Lawrence of Nasdaq disagrees with. “The Nasdaq-100 index has…consistently performed substantially higher when compared to leading US Large Cap Growth benchmarks,” she wrote in an emailed response to Barron’s. She did not comment on the index’s listing fees. Likewise, Invesco cited performance data when responding to Barron’s. However, investors should look beyond past performance when choosing an index to purchase. Rather than “performance chasing,” says Rodney Comegys, head of Vangauard’s Equity Index Group, investors should “have a sound investment reason for doing it.” They should also beware of “reversion to the mean,” when stocks that past outperformances then go on to underperform.

And while the Invesco QQQ ETF is categorized as a Large Growth index fund by Morningstar, the fund excludes major players like Salesforce, Visa, Mastercard, and Oracle because those companies aren’t included in the Nasdaq. But many of the excluded companies are included in Jackson’s preferred ETFs, which also have cheaper annual fees than QQQ’s 0.20%. And rather than charging listing fees, many other popular indexes use a quantitative selection process in order for a stock to be included in their benchmark, the article reports.