Researchers agree this effect is real. They do not agree on how strong it is, and that argument is still going on. So you can trust the direction, but not any exact number.
In the 1980s A&W believed it had found the move that would beat McDonald's. The Quarter Pounder had become an icon, so A&W answered with a third pound burger. More meat for the same price, and in taste tests people preferred it. In the market it failed, and for a while nobody inside the company could explain why. As A&W's former owner later told the story, the research surfaced something that has been repeated in marketing departments ever since. Customers felt cheated, and their reasoning was that three is smaller than four, so a third of a pound must be less than a quarter. The burger with more meat lost because its fraction looked smaller. This account comes from one man's memoir rather than published research, so treat the specific story with some caution. The underlying difficulty people have comparing fractions is separately well documented.
Customers are not evaluating your offer against objective truth. They are judging it in about half a second with whatever mental shortcut is closest to hand, and the shortcut does its own arithmetic. That is worth sitting with before you assume a better product will win on its merits. The way something is expressed, named or numbered is not decoration sitting on top of the value. For the person deciding in half a second, it is a large part of the value they think they are getting.
Source: Alfred Taubman recounted this in his memoir Threshold Resistance, 2007. A single account rather than published research. The underlying difficulty with fractions is separately documented.
Innumeracy
John Allen Paulos, 1988
On how badly people handle numbers, and what it costs when nobody notices.
Draw your own card. It does not take long, and it rewards taking your time.