Can I just say that some of the Usability 'equations' proffered to this thread bring tears to my eyes.
I look at this statement in terms of defining a causal relationship between usability & predictability. Or defining a set relationship. Essentially, Robert is saying that "everything which is usable is also predictable; and everything which is predictable is also usable." Some examples have already been provided that show the second part of the statement is incorrect - that some systems are alarmingly predictable in the way they suck. So, we're left with "everything which is usable is also predictable". A longer version of this statement might be: "an inherent characteristic of a usable system is that it behaves in a predictable manner in response to user interaction." Implied in this statement is that little or no learning should be necessary, although Robert does not explicitly make that constraint clear. Some have argued already that a system which is predictable in the first instance could better be characterised as intuitive rather than usable. Perhaps then we're looking to support the statement that: "*an inherent characteristic of a usable system is that, in response to user interaction, it behaves in a manner predictable by nominally experienced people*". Which now starts to introduce the notion of a continuum of predictability and usability which varies according to the experience of the user. Since, as a discipline, we tend to believe in the notion that completely novice users should be able to approach a system interface and interact meaningfully with it, we - in theory at least - support the notion of usability in the absence of predictability. In other words, the predictability or lack thereof is a characteristic of the user, not the system. We might then better characterise the relationship between usability and predictability as such: "an inherent characteristic of a usable system is that, in response to user interaction, it behaves in a manner that can be predicted with reasonable certainty by a person moderately experienced in the use of the same or similar systems". To put this in more succinct terms: "usability => consistency". And note that the relationship is one-way. Steve 2008/5/25 Robert Hoekman Jr <[EMAIL PROTECTED]>: > "Usability equals predictability." > > As in, if you can accurately predict what's going to happen next in an > interaction, it's because the action you're taking is understandable, > clear, > logical, makes you feel confident, etc. If you can accurately predict > what's > next, the interaction has high usability. If you can't accurately predict > what's next, the interaction has low usability. > > Shoot holes in that statement. <http://www.ixda.org/help> > ------------------------------------------------ Steve 'Doc' Baty B.Sc (Maths), M.EC, MBA Principal Consultant Meld Consulting M: +61 417 061 292 E: [EMAIL PROTECTED] UX Statistics: http://uxstats.blogspot.com Member, UPA - www.upassoc.org Member, IA Institute - www.iainstitute.org Member, IxDA - www.ixda.org Contributor - UXMatters - www.uxmatters.com ________________________________________________________________ Welcome to the Interaction Design Association (IxDA)! To post to this list ....... [EMAIL PROTECTED] Unsubscribe ................ http://www.ixda.org/unsubscribe List Guidelines ............ http://www.ixda.org/guidelines List Help .................. http://www.ixda.org/help
