According to Onestat, only 11.4% of all search queries are one-word phrases. 3 and 4 word phrases make up more than 50% of all queries (via Blog SEO). Surprisingly, even 4 word phrases surpass 1 word phrases by almost 50%.
It is also interesting to notice the cultural differences in the research – Canadians top search queries are 4 word phrases (24.02% of all queries) followed by 3 word phrases, while Germans clearly prefer 2 word phrases (making up 40.05% of all queries) followed by one word phrases.
All in all pretty strong proof that search engine marketers should invest primarily into multi-keyword phrases instead of standalone keywords.