The recommendations of Wall Street analysts are often relied on by investors when deciding whether to buy, sell, or hold a stock. Media reports about these brokerage-firm-employed (or sell-side) analysts changing their ratings often affect a stock's price. Do they really matter, though?

Before we discuss the reliability of brokerage recommendations and how to use them to your advantage, let's see what these Wall Street heavyweights think about Marathon Petroleum (MPC).

Marathon Petroleum currently has an average brokerage recommendation (ABR) of 1.74, on a scale of 1 to 5 (Strong Buy to Strong Sell), calculated based on the actual recommendations (Buy, Hold, Sell, etc.) made by 19 brokerage firms. An ABR of 1.74 approximates between Strong Buy and Buy.

Of the 19 recommendations that derive the current ABR, 12 are Strong Buy, representing 63.2% of all recommendations.

Brokerage Recommendation Trends for MPC

Check price target & stock forecast for Marathon Petroleum here>>>

While the ABR calls for buying Marathon Petroleum, it may not be wise to make an investment decision solely based on this information. Several studies have shown limited to no success of brokerage recommendations in guiding investors to pick stocks with the best price increase potential.

Are you wondering why? The vested interest of brokerage firms in a stock they cover often results in a strong positive bias of their analysts in rating it. Our research shows that for every "Strong Sell" recommendation, brokerage firms assign five "Strong Buy" recommendations.

In other words, their interests aren't always aligned with retail investors, rarely indicating where the price of a stock could actually be heading. Therefore, the best use of this information could be validating your own research or an indicator that has proven to be highly successful in predicting a stock's price movement.

With an impressive externally audited track record, our proprietary stock rating tool, the Zacks Rank, which classifies stocks into five groups, ranging from Zacks Rank #1 (Strong Buy) to Zacks Rank #5 (Strong Sell), is a reliable indicator of a stock's near -term price performance. So, validating the Zacks Rank with ABR could go a long way in making a profitable investment decision.

Zacks Rank Should Not Be Confused With ABR

In spite of the fact that Zacks Rank and ABR both appear on a scale from 1 to 5, they are two completely different measures.

Broker recommendations are the sole basis for calculating the ABR, which is typically displayed in decimals (such as 1.28). The Zacks Rank, on the other hand, is a quantitative model designed to harness the power of earnings estimate revisions. It is displayed in whole numbers -- 1 to 5.

It has been and continues to be the case that analysts employed by brokerage firms are overly optimistic with their recommendations. Because of their employers' vested interests, these analysts issue more favorable ratings than their research would support, misguiding investors far more often than helping them.

On the other hand, earnings estimate revisions are at the core of the Zacks Rank. And empirical research shows a strong correlation between trends in earnings estimate revisions and near-term stock price movements.

In addition, the different Zacks Rank grades are applied proportionately to all stocks for which brokerage analysts provide current-year earnings estimates. In other words, this tool always maintains a balance among its five ranks.

There is also a key difference between the ABR and Zacks Rank when it comes to freshness. When you look at the ABR, it may not be up-to-date. Nonetheless, since brokerage analysts constantly revise their earnings estimates to reflect changing business trends, and their actions get reflected in the Zacks Rank quickly enough, it is always timely in predicting future stock prices.

Is MPC a Good Investment?

In terms of earnings estimate revisions for Marathon Petroleum, the Zacks Consensus Estimate for the current year has declined 2.2% over the past month to $8.31.

Analysts' growing pessimism over the company's earnings prospects, as indicated by strong agreement among them in revising EPS estimates lower, could be a legitimate reason for the stock to plunge in the near term.

The size of the recent change in the consensus estimate, along with three other factors related to earnings estimates, has resulted in a Zacks Rank #5 (Strong Sell) for Marathon Petroleum. You can see the complete list of today's Zacks Rank #1 (Strong Buy) stocks here >>>>

Therefore, it could be wise to take the Buy-equivalent ABR for Marathon Petroleum with a grain of salt.

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This article originally published on Zacks Investment Research (zacks.com).

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