I have been researching this for well over three months and it appears that HP gives each word in the tittle a score based on the key words rate of search.
If the title has common words the score is lower, if the title has uncommon words then the score is higher; it appears to be based solely on the competition of certain key words/search engine SEO. It also depends on how many hubs with similar key words/topic have been previously published.
After the hub is published, then the score fluctuates depending on the number of visitors plus the key words SEO.
Again this is based on my own research with my own titles.