With two-thirds of the year over, it's a good time to look at the performance of the Dow Jones Industrial Average (^DJI 0.16%) and a few of its big winners and losers for the year. As for the Dow itself, the index is up 13.02%, even after a terrible August, in which the average lost 4.45% in that month alone. But despite August, the Dow has had a great run at it this year, with only two down months while moving higher during the other six. January was the best month of the year, as the index rose 5.77% and, other than August, June was the only down month as the average lost 1.36%.

A number of factors have played a role in why the markets have gone up and down this year, but so far the Federal Reserve has the hands down most powerful effect. For months now, market participants have waited for the Fed to start tapering its bond-buying program and every time it appears it will begin, stocks fall. And when it would seem the tapering will be pushed back, stocks rally as investors gain more confidence in the economy's ability to grow and strengthen with the government's support.

Now that you know how the Dow has done and why, let's take a look at a few of the big individual winners and losers of the year.

Losers first
Alcoa (AA) is the Dow's worst-performing stock year to date, as shares are down 11.29% since the start of 2013. Caterpillar (CAT 0.56%) is next, with the stock having fallen 7.89%. And the only other Dow component that is down since the start of 2013 is IBM, which has lost 4.84%. As for Alcoa and Caterpillar, these two companies have been affected by not only the slower-than-expected recovery here in the U.S. but also slowing economies all around the world. Europe is still struggling, China is slowing, Brazil and other parts of South America aren't wonderful. These slowing economies play on the revenues and profits of Alcoa and Caterpillar, which are both heavily reliant on strong construction and large infrastructure projects to help boost sales.

Additionally, they have been hurt by lower commodity prices. While Alcoa obviously needs aluminum to sell at a high price to help it out, Caterpillar typically sees higher sales in its mining equipment unit when precious metals or mined raw materials are selling at a premium -- again, another area that would normally help the two but hasn't this year.

When it comes to buying shares of either company, I personally would stay away from Alcoa while being patient with Caterpillar. Alcoa is in a commodity-driven industry and truly has no way of setting itself apart from the competition. Every other aluminum producer is selling the same thing and some of those producers are OK with losing money because their governments help support the business. That puts Alcoa in a position where the competition is selling the same thing for less than it can and it's still not going to go out of business, whereas you are.

But with Caterpillar, someone investing now needs to understand it may be a while before the company gets back on its feet when it comes to sales and growing those numbers. Today's share price also may look attractive on a price-to-earnings basis, but it may become more attractive in the future, so buying in thirds would be the best approach if you're convinced the Cat is a buy at this price.

The winners
The top two winners of the year thus far are Boeing (BA -0.33%), which has risen 37.9%, and Hewlett-Packard (HPQ 1.10%), which is up 56.77% year to date. While both companies may be the top Dow stocks, they have also had a very rough 2013. For Boeing, it has nearly all been due to its newest, crown jewel, the 787 Dreamliner. The plane boosts the best fuel efficiency in the air today, but in order to get that efficiency, it needs large batteries. And as many know, those big batteries can cause fires, which is one of the many problems Boeing has dealt with this year. An actual plane on fire on the tarmac, a number of emergency landings, smoke coming from another plane, faulty wiring with the fire extinguishers -- the list goes on. But investors and airlines continue buying stock and planes from the company and the shares just keep going higher.

As for Hewlett-Packard, the first half of the year was great. The company was ahead of schedule with its planned turnaround, confidence within management was high, and although PC sales were still struggling, it really looked like HP would soon be profitable because of progress made in other divisions. But that all ended recently when it announced its second-quarter earnings report and CEO Meg Whitman told investors that the company will not likely grow sales and profits in 2014 as it had previously hoped to do. That comment and a few others about the business sent shares tumbling 15.21% during the third week of August and well off its 52-week high of $27.78 per share.

As for either Hewlett-Packard or Boeing as an investment option at this time, I believe HP still has some room to run higher in the future, but investors once again would need to be extremely patient, as Whitman's turnaround plan may not fully play out for another few years. In the meantime, though, buying in thirds as the stock will likely continue to be rather volatile would be the only way I would start opening a position. As for Boeing, as long as the company fixes the problems it's been having without any major issues, (i.e., a plane crash), the stock should continue to do just fine and orders will likely continue to roll in from the airlines.

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