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16 CHAPTER 1 Introduction to HCI research

In HCI, there are some situations where the evidence over time supports a spe-
cific finding. One clear example is the preference for broad, shallow tree structures
in menu design (see the “Depth vs Breadth in Menus” sidebar). Multiple research
studies have documented that broad, shallow tree structures are superior (in terms of
user performance) to narrow, deep tree structures.

DEPTH VS BREADTH IN MENUS
Multiple research studies by different research teams, throughout the history
of the HCI field, have examined the issue of the trade-off between depth and
breadth in menus. Generally, tree structures in menu design can be implemented
as narrow and deep (where there are fewer choices per level but more levels) or
as broad and shallow (where there are more choices per level but fewer levels).
Figure 1.1 shows three menu structures.

(A) (B) (C)
FIGURE 1.1
Types of tree structure in menu design: (A) narrow-deep: three levels with two choices
at each level, (B) broad-shallow: two choices followed by four choices, (C) broad-
shallow: four choices followed by two choices.
The research has consistently pointed to broad, shallow tree structures as
being superior to narrow, deep structures. There are many possible reasons:
users get more frustrated and more lost, the more levels they must navigate;
users are capable of dealing with more than the 7 ± 2 options often cited in the
research literature (since menus deal with recognition, not recall), and strategies
for scanning can lead to superior performance. Different research methods and
different research teams, examining different users, have all come to the same
conclusion. So over time, the superiority of broad, shallow tree structures has
become well-accepted as a foundation of interface design. Some of the better-
known articles on this topic include:

Hochheiser, H., Lazar, J., 2010. Revisiting breadth vs. depth in menu structures
for blind users of screen readers. Interacting with Computers 22 (5), 389–398.
Kiger, J.I., 1984. The depth/breadth trade-off in the design of menu-driven
user interfaces. International Journal of Man-Machine Studies 20 (2),
201–213.
Landauer, T.K., Nachbar, D.W., 1985. Selection from alphabetic and
numeric menu trees using a touch screen: breadth, depth, and width.