Why They Scan
Jakob Nielsen

More research is needed to truly know why 79 percent of Web users scan rather than read, but here are four plausible reasons:

• Reading from computer screens is tiring for the eyes and about 25 percent slower than reading from paper. No wonder people attempt to minimize the number of words they read.
• The Web is a user-driven medium where users feel they have to move on and click on things. One of our users said: "If I have to sit here and read the whole article, then I'm not productive." People want to feel that they are active when they are on the Web.
• Each page has to compete with hundreds of millions of other pages for the user's attention. Users don't know whether this page is the one they need or whether some other page would be better: they are not willing to commit the investment of reading the page in the hope that it will be good. Instead of spending a lot of time on a single page, users move between many pages and try to pick the most tasty segments of each.
• Modern life is hectic and people simply don't have time to work too hard for their information. As one of our test users said, "If this [long page with blocks of text] happened to me at work, where I get 70 emails and 50 voicemails a day, then that would be the end of it. If it doesn't come right out at me, I'm going to give up on it."
  

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