Breadth vs. Depth

Breadth vs. Depth

by Dr. Bob Bailey

April, 1999

Breadth vs. Depth 1

After arriving at your Web site, what is the maximum number of mouse clicks a user should have to make before getting to useful information?

Ever since Miller's totally misunderstood "7" article, people have been watching for another good number. Currently, one of the main candidates has to do with identifying the maximum number of mouse clicks. Is it 2, 3, 4 or the magical 7?

Zaphiris and Mtei surveyed the old "breadth and depth" literature related to menu design to determine whether it was better to have a few pages with a large number of links appearing on each page, or to have more pages with fewer links per page.

In general, the "breadth and depth" menu research suggests that it is better to have more items at each level, and fewer levels. In their study, they found the same. The fastest performance came from having a web site with two levels, i.e., requiring two clicks.

Breadth vs. Depth 2

Larson and Czerwinski (1998) also considered the breadth and depth issues. They summarized the past research as finding that "most studies found that breadth was better than depth for organizing menu structure." In their study they compared web sites that had two levels with those that had three levels.

They reported that the 2-level web sites enabled reliably faster searches than the 3-level site.

It appears that the new magic number for system designers is "2".

References

Larson, K. and Czerwinski, M., Web page design: Implications for memory, structure and scent for information retrieval, CHI 98 Conference Proceedings, 25-32, (1998).

Zaphiris, P. and Mtei, L., Depth versus breadth in the arrangement of Web links, (1998) original paper.