(Percentage 'no fault found' in modern high-volume consumer electronics, from Brombacher et Al. (2005))

Up until the mid nineties quality managers in consumer electronics were doing great. Product quality was increasing, and - as a consequence - complaints were dropping. And then something weird started to happen: complaints as well as product returns were going up again. What was going on here? An investigation of the returned products revealed that the products were fully functional. To be able to reveal the source of  problems, customer support and repair centers have detailed categorization schemes to indicate where in the product the source of the problem lies. However, if a consumer returns the product for any other reason it is filed under one category: 'no technical fault detected'. Which technically speaking is true, but it really doesn't help you the clean up the mess.

The reasons for product returns?
A while ago, Elke den Ouden got a PhD on this subject, with a thesis called 'Development of a Design Analysis Model for Consumer Complaints', which caused quite a stir in the press [1, 2]. She investigated this 'no fault found' category, which are also called 'soft problems'; technically there is nothing wrong with the product, but still consumer complain, return the product or think the product is broken. Den Ouden pointed out that there might be several reasons for these soft problems, among which:

• People might expect the product to do more than it really does. I once heard of a consumer returning an mp3 player to the store because 'there was no music on it'. The sales person had a pretty hard time explaining to the (somewhat elderly) customer that he needed a computer to put music on the device.
• Consumer are less tolerant to products they don't like and return them to the store. Some retail chains, for example in the US, have a no-questions-asked return policy. Which allows you to return any product within a given timeframe. Poor usability might be one of the dissatisfiers, but you can imagine a whole range of reasons.
• Finally, some people return the product because they simply can't figure it out, or actually think it is broken because they are not operating it as intended.

Unfortunately, in a lot of the press coverage of Den Ouden's research, only the last of three options was named, such as in this article in Appliance Magazine:

A recent study by Elke den Ouden of Philips Electronics found that at least half of returned products actually had nothing wrong with them—consumers simply couldn’t figure out how to properly use them.

This might have been due to a Reuters piece on the subject, which had the headline 'Complexity causes 50% of product returns'. Which is technically true, but people seemed to interpret that as 'Poor usability causes 50% of product returns'. Talking about soft problems... For the distribution of soft problems that Den Ouden found, take a look at this paper (pdf).

softreliability.org
In her research, Den Ouden could not point out the distribution of causes of soft problems. At the Technical University of Eindhoven (TU/e) in The Netherlands, there is now a research project in progress called Soft Reliability, to explore the categories of soft problems and the factors in product development process that lead to them. I would recommend the publications section, where you'll find PDFs of a number of articles on the subject.

A new ally for usability specialists
So, quality engineers are running into the human factor. They are entering the field of usability, user satisfaction because practice is pointing them that way, whereas most usability specialist started out from what may best be called a 'belief system'. Maybe interaction designer, and usability and usability engineers have found a new ally. It's just a matter of time before we get the first Design for Six Sigma Usability tools.

See Also:
> Accenture Analyses Product Returns, But Fails to Explain How
> Product Complexity Causes Product Returns