NEW YORK (MarketWatch)—Apple Inc. is finally being added to the Dow Jones Industrial Average today, after years of speculation and hype. But, for investors, the excitement may be fleeting.

Historical data show share prices only briefly rally on the announcement that a company is being added to the exclusive, 30-member index--then fall in the weeks after its official induction.

In fact, there is a “clear pattern” of good performance leading up to an addition, then “bad performance following,” said Jason Goepfert, president of Sundial Capital Research, who analyzed stock-price trends of the last 20 DJIA additions during the 20 days before their addition and 20 days after. Of course, some of the declines may be due to mean reversion.

Since Apple’s AAPL, +3.03% closing price of $126.41 on March 5, the last day of trade before the Dow 30 announcement, shares of Apple have risen a slight 0.5%, though they are down about 0.3% to $126.75 in recent trade, hours ahead of its planned induction after market close on Wednesday.

Sundial Capital Research

Bernstein Research analyst Toni Sacconaghi said companies added to the Dow have historically outperformed the S&P 500 by 3% in the 30 days after the announcement of their inclusion--though Apple has so far been an exception to this rule--its stock not yet outperforming the S&P 500, which is up 1.5% since March 5. Sacconaghi said this usually indicates “incremental demand for shares” immediately after the Dow 30 announcement.

Apple’s seven-for-one stock split last June opened the door to the stock’s inclusion in the Dow and put it in line with virtually all of the DJIA eligibility criteria, which includes demonstrating “sustained growth,” being of interest to a large number of investors, and being a large-cap stock priced similarly to the other Dow 30 components in the price-weighted index.

Its inclusion follows a four-for-one stock split at Visa, which brought down the collective average of the price-weighted DJIA, thus sparking a need for a pricier stock, according to an announcement by the S&P Dow Jones Indices Index Committee.

See:The stock splits that paved the way to Apple’s joining the Dow

Apple is the biggest company in the U.S., with a $736 billion market cap, but its share price as of this writing was just $128, which would make it only the sixth most expensive stock in the Dow 30 behind Visa Inc. V, -2.54% , Goldman Sachs GS, -0.44% , IBM Corp. IBM, -2.04% , 3M Co. MMM, -4.83% and Boeing Co. BA, -2.97% —though Apple’s stock trades at a 272% premium to AT&T’s T, -1.03% stock, which it is replacing.

Apple gives the Dow its first taste of next-generation tech, which has been glaringly absent from the index even as companies like Facebook Inc. FB, -1.73% , Google Inc. GOOGL, -1.44% , Amazon Inc. AMZN, +0.18% and Apple pioneered massive innovation in mobile communication, e-commerce and social media. Those four companies have a collective market cap of roughly $1.53 trillion, which equates to roughly 30% of the entire Dow Jones Industrial Average—though only Apple and Facebook have share prices in line with the DJIA’s historical weighting standards.

Even Intel Corp. INTC, -0.34% and Cisco Systems Inc CSCO, -1.93% were added at a time when PC penetration was less than smartphone and tablet penetration is today. In fact, some might argue that the last major tech-sector nod from the Dow came in 1999 when both Intel and Microsoft Corp. were added in the same month. Apple will replace AT&T Inc., whose stock as of Thursday close was priced at $34, giving the mobile carrier a $176.5 billion market cap.

See: AT&T’s stock could beat Apple’s now that it’s out of the Dow

If Apple had been added in 2014, as some had expected, its performance would have ranked second among both tech stocks and all 30 Dow components, behind Intel. IBM, on the other hand, fell 18%, making it not only the worst tech-sector performer in the Dow 30 in 2014 but also the index’s worst stock overall. AT&T shares are up 5% over the last 12 months.

Interestingly, Intel and Microsoft saw brief stock-price rallies after their respective additions, but both tanked shortly after in the dot-com crash. Neither has returned to its heights of 1999-2000.

Don’t miss:The Nasdaq that hit 5,000 in the year 2000 was a very different stock index than the one that hit 5,000 this week

A version of this story was published on Dec. 26, 2014.

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