Simply adding a link into your text like this is NOT considered citing a source.
To cite this webpage properly, use an in-text citation like the one in this sentence (Plagiarism.org, 2012).
And then cite it completely in your bibliography:
How do I cite sources? (2012). Retrieved from Plagiarism.org at http://www.plagiarism.org/plag_article_how_do_i_cite_sources.html
Statistics are considered primary sources. These are the raw numbers you can use to help see trends and corrolations. Polls only survey opinions of people. They are not as credible as statistics, but they can help your research.