Most investors understand that the Dow Jones Industrial Average (DJINDICES:^DJI) is a price-weighted index, making it unusual among market benchmarks. But after serving the Dow well for decades, the price-weighting model has started to create bigger problems. What's behind the change?

In the following video, Motley Fool Director of Investment Planning Dan Caplinger takes a closer look at the Dow's price-weighted model with an eye toward identifying why it has become more of a problem lately. Dan points out that in the past, the index's high-priced stocks conducted stock splits to keep their share prices down, reducing their relative influence in the average. But in the past decade, that trend has changed. IBM (NYSE:IBM), which was the most heavily weighted Dow stock until the index's component shift earlier this week, hasn't split its stock since 1999. Chevron (NYSE:CVX), which also has a high share price, hasn't split stocks since 2004, while 3M has gone a full decade without a split despite its triple-digit price.

Dan examines the reasons why stock splits have fallen out of fashion, noting the rise of exchange-traded funds and online brokers that have largely made the traditional 100-share round lot a thing of the past. He notes that high-priced new Dow entrants Goldman Sachs (NYSE:GS) and Visa (NYSE:V) have never done a stock split -- and neither seems to have any intention of doing so in the future. Yet unless they and other high-priced stocks execute splits, the Dow will continue to have big disparities in weighting among its components.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.