layout - Odd or even number of products per row on a product listing page?

I heard from a reputable source that on e-commerce websites, users find it easier to choose a product when there is an odd number of items in row, as compared to an even number.

In their experience, 3 or 5 products tested better than 4, for example. Sure enough - I can find plenty of sites with 3 or 5 products per row, but I can also find plenty of sites with an even number too.

So given that everything else remains the same:

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  What actual evidence is there for an optimal number of products per row being related to the odd/even nature?

  
  
  


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  How/why does this affect the ease with which customers can make a decision?

  
  

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Answer

An example of this claim can be found in Smashing UX Design: Foundations for Designing Online User Experiences - page 300, point 2. It says that an odd number of products:

• can be easier to scan,


• makes the choice easier to make,


• keeps the eye moving across a row because the items cannot be grouped easily.

It suggests that this might be backed up by the "rule of odds" (see on Wikipedia and here, and on photoSE). The claim is that an odd number of objects is more interesting and natural, or even more pleasing and attractive.

I think the problem might also be connected with the issue of 5-star ratings (from 1 to 5). Some claim that people tend to choose the neutral, middle option because it's easier and therefore there should only be an even number of stars to force a more meaningful choice (others disagree). Perhaps you do want to make the choice easier on an e-commerce site.