During their budding years, that is, around the turn of the century, successful SEO and Internet marketing simply meant stuffing your title, description and keyword tags and the content area with the relevant keywords and having a high keyword density.
However, over a period of time, when keyword density became more of an SEO trick than an SEO tool, for getting a high rank, it lost all relevance for the search engines. Sure, it is still needed but it’s not the only thing that would get you a high ranking.
If you want a real case study as a proof for it, you can take my case. I do not really care about the keyword-density when writing my content. My articles hardly have a keyword density of 2% and still they work fine for me. This shows whether I have a 2% keyword density or even lesser than that, rankings of my content pages would not really suffer simply because of that.