This article first appeared in The Ergonomics Report™ on December 19, 2012. It is republished here, with permission, as an open access Ergonomics Today™ article, with minor updates.
Researchers Anna Pereira, David L. Lee, Harini Sadeeshkumar, Charles Laroche, Dan Odell, and David Rempel published the results of a study they conducted to investigate the effect of key spacing on typing speed, error, usability, forearm muscle activity and wrist posture. They identify this as Part 1, with Part 2 to be published at a later date. The study focused on conventional mechanical keyboard design, not software generated on-screen keypads such as those seen on mobile computing devices. This article is a summary of their research and findings.
Pereira et al indicate that conventional keyboard key spacing may be influenced more by industry practice and earlier research from the 1970’s than it is by ergonomics issues like typing speed, biomechanics, error rates and usability. They note that International Organization for Standardization (ISO) and American National Standards Institute and Human Factors and Ergonomics Society (ANSI/HFES) each recommend that the horizontal and vertical center-to-center distances (when viewing a keyboard from above) each be 19 mm +/- 1 mm, though not all keyboard designs abide by these standards.
For example, as laptop/notebook computers have become smaller, so have some keyboard designs, which create some advantages, for some people and organizations, including:
For the most part, though, most keyboard key spacing, even for laptops/notebooks, abides by the conventional 19 mm standard.
Pereira et al also review the findings of the relatively few other studies that have looked at performance related to key spacing, including these previous findings:
None of the above studies considered key spacing effects on biomechanical or physiological measures.
Recognizing that people with smaller fingers would likely adapt better to smaller spacings, Pereira et al focused on people with larger fingers, and in this Part 1 article they primarily examine horizontal key spacing (vertical spacing will be reported in their future Part 2 article).
The following discussion of study methods is significantly abbreviated, and interested readers are directed to the complete article, cited below.
Again, interested readers are directed to Pereira et al’s complete article for full details, but their results include:
What This Might Mean to Ergonomists
This is the kind of research that is very important at the consumer product design level, but it may seem esoteric, or it’s value may not seem readily apparent in the everyday practice of ergonomics. On the design level, it’s hard for me to believe, but not at all surprising, that for the past 30 or more years something as important as key spacing on a keyboard has been driven by manufacturer convenience and unfounded conventional wisdom. I applaud Pereira et al for stepping up to finally apply a human centered research and design approach — ergonomics — to something as ubiquitous as the keyboard, and look forward to their Part 2 publication. This kind of research will be valuable in the formulation of future keyboard design standards, and those standards will finally be based on human/user performance requirements instead of technical, manufacturing and market convenience.
On an everyday application level, however, you may have heard the phrase “I fat-fingered it,” meaning the person missed the button, target, or in this case the proper keyboard key and made an error, placing the blame on user error rather than poor design. This study provides scientific evidence for the “fat-finger” effect.
This study should also cause us to reflect on the “one-size-fits-all” keyboard design (or any other one-size-fits-all design). Such designs rarely, if ever, fit all well, and often, in fact, fit few well. As Pereira et al point out in their review of their and others’ research, people with smaller fingers may benefit from less key spacing, while those with larger fingers may benefit from greater spacing. Will we see a trend toward different keyboard designs for different sized people? Is this something that ergonomists should begin advocating, or is the on-size-fits-all approach “good enough” when it comes to keyboard design?
In the mean time, for “standard” keyboard design, Pereira et al offer this advice:
On the basis of these findings, keyboard designers are encouraged to consider designing keyboards with horizontal and vertical key spacing of 17 mm or 18 mm to gain the benefits of smaller keyboards (e.g., smaller and lighter laptops, reduced cost to manufacture, better usability for smaller users, and reduced reach to the computer mouse) while still accommodating the needs of typists with large fingers.
Anna Pereira, David L. Lee, Harini Sadeeshkumar, Charles Laroche, Dan Odell, and David Rempel, (2012). The Effect of Keyboard Key Spacing on Typing Speed, Error, Usability, and Biomechanics, Part 1. Human Factors, published online before print, December 6, 2012, doi:10.1177/0018720812465005.
At the time of this writing, the complete article was available to Human Factors or Sage Publications subscribers at: http://hfs.sagepub.com/content/early/2012/12/04/0018720812465005.full