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This usually comes down to 2 questions:

• How many trees are we testing at a time?

• Are we testing the whole tree, or just part of it?

How many trees?

If we’re testing an existing tree for problems, before starting our IA redesign, the answer here is simple – we’re testing just the one tree.

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For more on testing alternative trees against each other, see The design phase: creating new trees in Chapter 3.

Which part of the tree?

If we’re testing a small or medium-sized tree (say, less than 500 items), we will normally test the whole tree – no major pruning required.

If our tree is larger (say, 500-1000) items, we have 2 options:

• Test the whole tree – Easy to prepare, but affects how many tasks we can ask each participant.

• Test a “pruned” version of the tree – Takes some effort on our part, but lets us concentrate on the parts we’re really interested in.

Finally, if our tree is very large (more than 1000 items), testing the whole tree may be feasible, but in most cases we recommend pruning the tree to keep the participants’ effort from becoming onerous.

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