Imagine that you’re a researcher who wants to investigate the effects of narcissism. The standard for evaluating narcissism is a questionnaire called the Narcissistic Personal Inventory (NIP), in which people are asked which of a series of phrases best describes them. Question 5, for example, asks whether you identify more with the answer "The thought of ruling the world frightens me" or "If I ruled the world it would be a better place."
The NIP stresses that there are no right or wrong answers. And while many of the traits it measures are usually considered undesirable (exploitiveness, vanity), others are not (authority, self-sufficiency). But the test's motives are still very transparent, which would make most potential participants wary of taking it.
This was the dilemma faced by several academics researching the performance of companies run by narcissistic CEOs. Their solution? Measure the size of the CEOs’ signatures on documents they filed publicly with the Securities and Exchange Commission. The bigger the signature, the more narcissistic the CEO.
For the rest of the story: http://priceonomics.com/the-surprising-way-psychologists-measure/