Web site owners might be amazed to learn that one of the biggest sources for duplicate content isn't externally, but rather internally.
Certainly, popular sites and blogs that syndicate a lot of content have to deal with external duplication, but as I already touched on external duplicate content, we know that there are steps to minimize those challenges and to establish your site as the canonical source.
Internal, or on-site, content duplication tends to come in a few key ways, the first of which is within the key page elements. The second is from the content itself; similar to e-commerce sites using stock product copy, you may be using your own copy over and over again on your site. Third, it simply may come from too little differentiated copy.
More often than not, sites end up repeating the title tag, page after page. Making matters worse, the meta description is the same on all of these pages. At this point, even if the H1 tags are different on these pages, it may not be enough to convince the search engines that these pages are different--or different enough. If you do nothing else, at least avoid duplicating page titles at all costs.
In the second example, perhaps you have product, blog, or press release snippets throughout your site. Maybe these exist in a sidebar area of your site. Hopefully, these are secondary elements on the page, so there is still quite a bit of copy on the page, allowing it to stand on its own. But if the pages these snippets appear on have very little additional content, this repeated content may start to dilute the differentiation between these pages.
You may find that a few of these pages drive far more traffic than the others. Perhaps the search engines see these as duplicates, and therefore are just selecting the one page to return in search results.
The other example is also seen quite frequently with e-commerce sites, particularly at the product page level. Let's pretend you have an electronics site on which you are trying to sell some of those cool little gadgets that we have come to adore. You have sections on digital cameras, video cameras, and MP3 players.
You're all about providing the best experience for your visitors, so you've pulled together some great content on how to select and use each of these devices. Rather than having your visitors click on a link to get to this additional content, you've included the appropriate content on each of the product pages.
So when someone is looking at the product page for that one particular digital camera, in addition to product details and write-up (hopefully unique and not stock copy), you also include your information on how to select a digital camera. Unfortunately though, there may be more of this helpful how-to information than product information. Now all of your digital-camera product pages may look an awful lot alike.
What to do? This is a challenging one, since there may not be a whole lot of information on these pages otherwise. At the very least, you'll want to be doubly sure that all of the page titles and headings are unique (as mentioned above).
Be sure to incorporate distinctive details, such as the brand and model name and number, or color, if each product has its own color page. That said, if the only distinction between three pages is "black," "silver," and "gun metal," you may be better off combining those to one page. Then again, perhaps those pages could drive more long-tail searches as standalone pages.
As you can see, it isn't always a black-and-white answer. You may need to test and turn to your server traffic logs or analytics to really understand the best choice to make.
Unless you can customize the additional how-to information on these product pages enough, you may be better off linking to a special-guide section on your site. The good thing is that you can really strengthen these guide pages with rich anchor text.
If all of your digital camera product pages include the link "How to select a digital camera," that sends a strong signal to the search engines that the destination page for that link is all about how to select a digital camera. And with this how-to page being more informational in nature than commercial, you may also be able to drive external links, as well, if you've really created an excellent how-to guide.
An interesting tool, giving you a feel for how similar search engines may view two different pages, is this online duplicate-content tool. While we may not know what the tipping point is for being considered duplicate, and each search engine may vary anyway, with a little research and testing, you might be able to establish rules or guidelines for your own site.
Stay tuned for a wrap-up of the discussion on duplicate content, with what I'd safely say is the biggest challenge nearly every site faces with duplicate content. Fixing it may yield the greatest reward across a number of different areas.