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From: palan-t@acsu.buffalo.edu (thiagarajan palanivel)
Newsgroups: comp.human-factors
Subject: Re: Individual Differences
Message-ID: <81378@eerie.acsu.Buffalo.EDU>
Date: 27 Jun 91 00:53:55 GMT
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Scott McGregor writes:
 
>Will people be doing the same task different ways?  How do you correct
>for the fact that the number of possible errors that a user can make are
>large in a command language (typographical errors, choosing missing
>objects, etc.) which are not possible in more constrained menu or direct
>manipulation systems (e.g. no typographical errors possible in menus,
>since there is nothing to type, no selection of missing objects possible
>in direct manipulation because they aren't presented)... Or is tolerance
>for errors part of the cognitive skills that your are trying to compare
>against?
 
>Scott McGregor
>Atherton Technology
>mcgregor@atherton.com

Yes, people will be doing the same task in different ways.

The essential issue in this research is the commission of (and recovery from)
errors. 

On the one hand, there is the issue (expressed in your post) of possibly 
trading off potential for error with "power". Yes, there is greater 
potential for error when using command languages (when compared to Menus 
and Direct Manipulation), but there is also, as you put it, less 
"constraint" in terms of the actions the user can perform, and the objects 
that these actions can be performed on. The real issue in this case is, is 
this trade-off the same for all users. Are all users equally error-prone in 
each environment ? If they are not, then the trade-off doesn't have the 
same relative magnitude for all users. There may be therefore, an interface 
that optimizes this balance for a particular user. And the optimal 
interface for another user may be different. If such unique optimal designs 
exist for each user, the cognitive profile of the user must play a 
significant (if not the sole) role in their determination.

Incidentally, I have met several people who do not accept that such a 
trade-off exists. Rather, they feel that there is relatively little 
difference in the error potential of different interfaces. The errors (or 
even relative speeds of performance of actions in different modes) that 
are possible are just different in nature, and are directly dependent on 
the nature of the interface. Such an argument is based on the classical 
breakdown of errors into the categories of slips and mistakes (a la James 
Reason and Donald Norman), and the cognitive analysis of errors in each 
category. Personally, I feel that this method of error classification itself 
is not comprehensive enough, but that's another issue.

On the other hand, and perhaps much more important to the validity of this 
work, previous research shows beyond a doubt that the greatest 
source of variability in performance (in terms of time to perform a task) 
between users is the commission and recovery from errors. Without the 
effects of errors (error-free task performance time), a 2:1 ratio usually 
covers the whole range of subjects' performance in experiments. With error 
times included, the ratio of best-to-worst performance is commonly in the 
10:1 to 50:1 range for such tasks as text-editing, programming, and 
information search. (Egan, 1988 (referenced in my initial post) covers this 
aspect extensively).

At a more fundamental level, I think that these results indicate that while 
perceptual limitations may be the limiting factor for users in general, 
cognitive limitations account for most of the variability between users.

Raj Palanivel
Dept. of IE
SUNY@Buffalo
(716)-636-2357