Google Panda is a filter first launched in February 2011, resulting in a change of Google search results ranking. It was predicted to affect 11.8% of all queries, although there is no way of knowing exactly what did Google change. What we know is that Google Panda was targeting low quality websites with the purpose of reducing their ranking and subsequently increasing the ranking of higher quality pages. Fortunately for penalized sites, Panda is updated time to time, so affected web sites can regain their ranking if they corrected the issues.
In order to see whether your site got penalized or not, you can compare data from Google Analytics the days before and after the launch of the Panda Update. If you exclude branded keyword generated traffic, you might get an idea about the situation. Comparing multiple sites which got penalized, SEO experts were able to establish the criteria Google used for this particular update. Sites that had excessive advertising, sites with low quality design, those who had their user generated content from low quality websites and those who had less usable content were among the penalized ones. If you were using duplicate content from other websites or from your own subdirectories, or if you had a poor visitor interaction, you were probably hit by Panda. On the other hand sites with easily readable, unique and attractive content received a higher ranking after the update.
What all webmasters should understand is that the purpose of every Google update is not to penalize sites, but to offer its users access to higher quality content, by listing those sites first. So if you were hit by Panda, you should be interested in how to correct the problem and regain your ranking and traffic. First of all you can check whether your site is using duplicate content. You can do that by using CopyScape.com, a tool which allows you to check the web for duplicate content. If you identified such problems you should remove the duplicate content and replace it with original, unique and useful content. If you have duplicate content within your own website, either resulting from the automatic creation of hundreds of pages with the same content or by having pages with multiple URLs, those have to be removed too.
Link quality, link volume and link velocity are elements considered by Google when establishing the ranking of a particular site. That is explainable considering that in order for someone to organically want to link to your site you must have original, unique and relevant information or offers better than those of your competitors. If you don’t have any of that, but you still need the links to increase your ranking, there are several ways of getting them. Links, questionable in quality and value, can be built, bought, borrowed or even stolen. Such techniques might have short term benefits, temporarily increasing the ranking of your site. However, once Google performed a check, you will be penalized and your traffic can easily drop beyond initial levels. On the other hand if your visitors spend more time on the site, take actions there or repeat their visits, those will be considered trust algorithms by Panda.
Even if you think you found the reason why the Panda Update affected your traffic and you already corrected it, you might still have surprises. Panda is a rolling algorithm, meaning it is constantly changing. Every time a new update is released, web sites will be affected. If that is your case, you should contact a SEO specialist for a Google Panda Audit, to understand why your site got penalized and how to avoid further penalties.