Yandex says it doesn’t use keyword density as part of it’s ranking algorithm. The company says it looks at the quality of a web page and makes an assessment based on that instead.
Below is a statement from Yandex:
The question if we take in account keyword density is not correct. We don’t operate with keywords in our search at all, but only with text fragments (possible synonyms) extracted from full texts of documents.
Yandex looks at each page individually, and performs a detailed analysis of the text. It then makes an assessment based on this analysis – this is how it ranks web pages. If you want to rank high in the search results for specific keywords, then you need to write articles that are high quality, provide relevant information and are interesting to users; in other words – high quality content.