Singular Keywords Shown To Have Influence
Consider the terms "weight" and "weights"; to a fitness nut, they may signify different things, and in many markets, it’ll matter whether you optimize for singular or plural forms of keywords. A look at Google Trends data throws into question the idea of going plural by default.
Run any pair of words you like through the system. Whether the subject is iPod(s) or puppy dog(s), the line representing the plural form almost always shows up beneath the singular form’s streak. Lower search volume should translate to less search traffic.
However, Ann Smarty points out, "Back in March Hitwise published its UK search report on differences between plural and singular keyword forms," and the report was "echoed by multiple bloggers enthusiastically encouraging webmasters to focus efforts on plural because plural form was proved to send more traffic."
So Smarty suggests, "Google is considering broad match – thus all the millions of possible phrases containing ‘laptop’ fall under [laptop] search."
Also, since the Hitwise report mainly focused on which keywords send the most traffic to shopping and classifieds sites, blogs and other entities not selling things shouldn’t necessarily be swayed by its findings.
It’s something to consider when trying to differentiate between fat on a body and iron on the floor.