RE: Broad and flat vs hierarchical facets - beginning with introducing

Bill asked:
>1. What is the practical maximum number of items that can be included in
>a flat (alpha or logically sorted) picklist before users won't use it or
>can't find the item they are looking for?

In my experience (in particular working on a clinical incident reporting 
system), I found this depends very much on the nature of the information 
presented. People will comfortably scroll through a list of countries to 
find their own (usually using keyboard shortcuts), but will not necessarily 
scroll through a relatively short list of less familiar items. In this 
scenario, countries are familiar to the user, they know immediately what 
they are looking for. The 'contributing factors' taxonomy was significantly 
shorter, but required the user to read and evaluate each option before 
making a choice.

Hierarchical structuring of the classification undoubtedly helps both at 
points of information capture and of information retrieval.

>2. In a hierarchical picklist, how many layers are considered to be
>practical and what is the practical maximum number of items that should
>be presented in a layer (assuming that the hierarchical logic allows
>much freedom to go flat vs deep)?

In high-fidelity prototype testing with a wide range of users, I have found 
more than two levels in a single picklist can be confusing, especially to 
inexperienced users.

I have more successfully split out hierarchical classifications into a 
series of picklists (ideally each acting as a filter for what is visible at 
the next level). This means that the user is narrowing the range of choices 
as they move down in the hierarchy and as such the task load of making those 
choices becomes lighter. E.g.:

[Range A-Z] [v]                    (User selects option B)
      [Range B1-B6] [v]            (User selects option B5)
           [Range B5a-B5e] [v]     (User selects option B5a)

The optimum number of levels here in the testing I have conducted is 3. 
Where I have needed to use classifications that go beyond 3 levels, I have 
designed the interface to separate the taxonomy into different questions 
(i.e. question 1 addresses levels 1-3; question 2 addresses level 4-6).

Hope this is helpful!

Best regards
Vanessa

vanessa wolfe-coote | experience architect

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