The Slow Tail: Time Lag Between Visiting and Buying

by Jakob Nielsen on September 6, 2005

Summary: Users often convert to buyers long after their initial visit to a website. A full 5% of orders occur more than 4 weeks after users click on search engine ads.

Dr. Alan Rimm-Kaufman from the Rimm-Kaufman Group recently tracked one million clicks on search ads on Google and Yahoo. These advertising clicks eventually translated into 41,377 conversions on the target websites. Although the clients in question must remain anonymous, they presumably have good sites since their conversion rate (4%) is twice that of average websites (2%).

B2C sites comprised 85% of the sample, leaving 15% for B2B. Conversions were mainly defined as actual sales, though a few sites used other definitions, such as catalog requests or other forward movement in more complex sales cycles.

Sales Cycle Delay

Once users arrived at the sites from the search engines, orders came fast and furious: half of the conversions occurred within 28 minutes. These are the people who know they want to buy something, and they'll give you the order if you have a good e-commerce site and a reasonable offer.

Although 75% of the conversions occurred within 24 hours, the last quarter took much longer to arrive. Orders didn't reach the 90% mark until 12 days after users had clicked on the advertisement, and it took four weeks to reach 95%. Thus, the last 5% of orders happened more than 4 weeks after the initial click.

The following chart shows the days required to reach a certain percentage of the ultimate conversions.

Percentile chart showing delay in orders, especially for the last 20% of sales (after the 80th percentile).

As the chart clearly shows, the curve breaks around the 80% mark. In other words, four-fifths of the orders happen quickly (within three days of the initial visit), but the last fifth constitutes a slow tail, where additional orders accumulate at a drastically reduced pace.

After two months, 99% of orders had been received; there was still one more percent to be gained during the third month.

The slow tail is more prominent for big-ticket purchases. For items costing less than $100, 90% of orders were received within 11 days. For items costing more than $300, it took 18 days to reach that level.

Highly delayed conversions are a phenomenon I know well from my own business. People often tell me that they'd been reading the Alertbox for five years before they could convince their boss to pay for an independent usability review — admittedly a big-ticket purchase at $38,000.

The Slow Tail: Design Implications

  • If you conduct A/B testing or collect site metrics, you can't just analyze users' behavior during their first visit. A day's worth of data will capture only 75% of the results. And that's for the average site: if you're a B2B site selling expensive or complicated products, the first day will bring an even smaller percentage of the desired actions.
  • Similarly, if you use cookies to track user visits, you must set at least a 90-day expiration date or you'll lose track of many conversions.
  • Users often return to a site multiple times before making their final decision. Your design must therefore support revisitation behaviors, which differ from initial visit behaviors. In particular, among the five quality attributes for usability, you might have to pay more attention to memorability — by keeping things in the same place, for example. (Of course, learnability is still paramount; there won't be any subsequent visits to a website that users can't figure out within a few seconds of their first visit.)
  • Don't make premature demands on users who aren't ready to buy. For example, don't require registration to read whitepapers or see a demo. If you do, you'll scare away many users who otherwise might have converted at a later date.
  • Don't time-out shopping carts. When users return, anything they had previously added to their carts should still be there. Same for any build-your-own configurators and user-created wish lists. If a customer indicates an interest in your products, don't throw away their work just because they haven't bought anything for a few weeks.
  • Retain the special landing pages for search ads and other campaigns for at least three months after the campaign ends. Users sometimes save brochures or bookmark URLs of ads for later perusal.

In general, the slow tail tells you that not all users are ready to commit on the spot. Don't rush them. Let users browse your site and gradually learn about your products, while making it easy for them to buy during future visits.

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