UK e-commerce sites are losing about £300m in lost sales every year because they are riddled with "invisible errors".
A study of sites by web testing firm SciVisum said the problem lay with errors that could not be detected by web analytics.
Total online sales for 2006 reached £30.2bn according to IMRG. SciVisum's Lost Online Sales Study revealed that 1% of online customer sessions experienced significant error numbers.
"This is a worrying trend for e-commerce and IT directors and for consumers with Christmas just around the corner. Poor performance and web errors will mean lost sales," said Deri Jones, CEO at SciVisum.
SciVisum investigated the performance of 40 online sites from the retail, finance, insurance and travel sectors, over a period of six months.
The study confirmed that customers of e-tailers are being exposed to a significant number and range of problems online, which prevent them finishing their sessions on the sites. The problems are invisible to existing tools and web analytics, said SciVisum.
"Invisible errors are not outages affecting 100% of users, but are problems that impact a percentage of users at any point in time. A problem that impacts say 1 in 100 random users on a particular journey is not reproducible by IT teams, and so frequently remains unresolved," said Jones.
SciVisum's testing involved visiting the site and attempting to make a "user journey" every five minutes throughout the day. This allowed the company to see what customers see, and made it possible to identify a range of intermittent problems that impact real users, but that are invisible to any other analysis. These problems include:
Session swap: where two users see each others' online sessions. Nowhere is this category of problem detected in server or analytic logs.
Page not delivered errors: because the page is not delivered, there is no log of the error in web analytics.
Jump back: the user is in error forced back several pages: the new page is itself a valid page, so no errors are logged in analytics or tech logging.
Page content incomplete: web analytics log only that a page was delivered, not whether it showed the user what they expected.
Shopping Basket errors: e.g. basket is empty after adding items. Nowhere is this category of problem detected in server or analytic logs.
SciVisum said firms should conduct similar testing themselves and that they should make sure that customer service teams are more tightly integrated with the IT departments behind the sites, as customer service teams often have a hint of ongoing problems from customer feedback.