New webmasters are often warned about duplicate content - what exactly is it? While most webmasters would agree on some aspects of this topic, others aren't quite as clear cut as to what kind of duplication will result in a search engine penalty or ranking reduction.
Multiple Page Duplicate Content. Sometimes webmasters choose to put the same content on different pages in the same site. It's far better to have just one page with that content and link to it as needed.
Query-based Duplicate Content. It's common on dynamic sites for duplicate content issues to exist. For example, the following two URLs may lead to the exact same page:
by linking to the same content in different ways, the potential search engine rankings for that content will probably be lower.
Cross-site Duplicate Content. This is a common issue when the same content is replicated on multiple websites. Sometimes, the same owner may re-use the content. Sometimes content can be illicitly copied without permission. Sometimes, multiple webmasters may use the same article with permission, not realizing that it has been used elsewhere. Whatever the reason, this content will probably be devalued by search engines.
How Similar is "Duplicate"? One of the often-asked questions is how similar does content need to be before it is flagged as duplicate. Is the same content on a different page structure (e.g., different navigation structure, header, footer, etc.) considered duplicate? Is changing a few words enough? While there's not a clear answer to this question, the general advice is to assume that the search engines will be smart enough to discard standard page content (headers, footers, etc.) when checking for duplicate content. Changing one or two words won't necessarily be enough, either - some experts use 70% duplication as a guideline.
As a general rule, avoid duplicate content if you don't want a search engine penalty (or lower rankings). If you must reuse previously published content, rewrite it, reorganize it, break it down differently... anything to keep if from being tagged as an obvious duplicate of another page or site.
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