last name effect
n. The closer a person's childhood surname is to the end of the alphabet, the faster that person tends to make purchase decisions.

Example Citations:
The last-name effect is a continuum, researchers found. So a Rodriguez will buy quicker than a Garcia. Those with last names in the middle of the alphabet make purchases with middling speed.
—Gregory Karp, "It's academic!," Chicago Tribune, February 18, 2011

E-mails were sent out to adults offering them $500 to participate in a survey. Average response time was between six and seven hours. The same negative correlation between response time and alphabetic rank was observed, but only when the researchers looked at the names the respondents were born with. When Carlson and Conard looked at married names or names changed for some other reason, the correlation dwindled to insignificance. This, they conclude, demonstrates that the "last name effect" derives from "a childhood response tendency." Only people who grew up with a name at the back of the alphabet demonstrated truly Pavlovian responses to the $500 offer.
—Timothy Noah, "Tyranny of the Alphabet," Slate, January 28, 2011

Earliest Citation:
This article links the speed with which adults acquire items to the first letter of their childhood surname. We find that the later in the alphabet the first letter of one's childhood surname is, the faster the person acquires items as an adult. We dub this the last name effect, and we propose that it stems from childhood ordering structures that put children with different names in different positions in lines.
—Kurt A. Carlson and Jacqueline M. Conard, "The Last Name Effect: How Last Name Influences Acquisition Timing," The Journal of Consumer Research, January 5, 2011

Another sense of this phrase is older, and it refers to the perceived tendency for economics professors with surnames closer to the start of the alphabet to get tenure more often than those with last names towards the end of the alphabet. Why? Possibly because economics papers list authors in alphabetical order rather than, say, priority order. Here's the earliest cite for this sense:

And then you get the last name effect:

—Archit, "Interdisciplinarity, Leiter and the Bluebook," Concurring Opinions, December 3, 2007

Related Words: