Now more than ever, investors who need income from their portfolios have come to rely on dividend stocks. Because bonds, bank CDs, and other traditional sources of income have largely dried up, even more risk-averse investors have essentially found themselves forced to try to find the highest-quality dividend stocks they can buy.

One common way that prospective dividend investors seek to distinguish high-quality dividend stocks from the rest is by looking at S&P's list of Dividend Aristocrats. By meeting select criteria, the companies on the Dividend Aristocrats list have demonstrated their ability to stand the test of time, surviving through good times and bad to keep consistently rewarding their shareholders.

Yesterday, S&P made regular changes to its Dividend Aristocrats lists. I'll review those changes later in this article, but first, let's take a closer look at how a stock becomes a Dividend Aristocrat and why it's such a select group.

Stick with dividend royalty
The first thing to understand about Dividend Aristocrats is that membership in its broadest list has nothing at all to do with the most common way that ordinary investors judge dividend-paying stocks: their yield. It's easy to focus on high-yielding dividend stocks, but the problem with them is that even though their yields may be high right now, there's no guarantee that their payouts won't go away in the near future. Moreover, high yields often result from beaten-down shares, and despite the value opportunities that some of those stocks present, often, share-price declines turn out to be prescient in predicting dividend cuts.

By contrast, Dividend Aristocrats require a long track record of annual dividend increases. Historically, that threshold has been 25 years for all of the Dividend Aristocrats lists. Last summer, S&P reduced the requirement for its High Yield Dividend Aristocrats, which include not only S&P 500 companies but also the mid-cap and small-cap companies included in its broader S&P 1500 index, to 20 years. But the requirement for the main S&P 500 Dividend Aristocrats list remained at a quarter century.

Whether you look at 20 years or 25 years, the track-record requirement guarantees that companies have to demonstrate the ability to increase dividends even during tough times. The financial crisis of 2008 thinned the ranks of the Dividend Aristocrats considerably, as many stalwart financial companies that had previously maintained solid dividend growth found themselves having to eliminate or severely cut their payouts, breaking their streaks of increases.

The new Aristocrats
Reaching the 25-year mark for the first time this year are three S&P 500 companies: Chevron (NYSE:CVX), Cardinal Health (NYSE:CAH), and Pentair (NYSE:PNR). The companies have a diverse set of backgrounds, and the quality of their recent dividend increases varies widely.

For instance, Chevron has greatly accelerated the pace of payout hikes over the past two years. In 2011, the company raised its dividend twice, with the increase totaling 12.5%. In 2012, Chevron made another double-digit percentage dividend increase of 11%. Similarly, Cardinal has increased payouts at a 10%-plus annual pace since 2005. Pentair, on the other hand, has been satisfied with $0.01- and $0.02-per-share raises throughout its history, with the stingiest yield of the trio at just 1.7%.

Departing the Dividend Aristocrats is Pitney Bowes (NYSE:PBI). The company didn't break its long streak of dividend increases, but its share price fell substantially enough that it triggered the requirement that a stock have a market cap of at least $3 billion to qualify. With an impressive yield of 12.8%, Pitney Bowes is still attractive to many dividend investors, but others believe that the company's plunging stock price reflects an inability to adapt to the near-demise of traditional mailing services.

Be careful out there
As Pitney Bowes' experience reveals, there's no guarantee that a Dividend Aristocrat will save you from big losses in your portfolio. But for the most part, the list is a good place to start your research in finding promising dividend stocks for your income portfolio.

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.