Task success rate

Just as we saw for the study's overall score, the most important thing to look at for a task is success rate – how many participants found the correct answer?

This is typically rated out of 10 or 100. For example, a score of 71 means that 71% of the time, participants arrived at a correct answer:

The same rough markers we used for overall scores hold true for individual tasks:

Success score	Meaning
0-50	Most participants had real trouble with the task. If they understood the task properly, then the tree failed to do its job. If they didn’t understand the task (see Where they went later in this chapter), then we won’t be able to judge the tree based on this task alone.
50-65	A mixed bag: most found it, but quite a few didn’t. This usually indicates that the tree is roughly right for this task, but there are specific topics that are luring some users off the correct paths.
65+	Most participants succeeded. The tree is performing well for this task, and probably only needs minor tweaks to corral the wayward few.

Success rate is a good general indicator of the effectiveness of our tree, but immediately we want to dig deeper. For example, if we have a success rate of 27% on a task, we naturally want to ask “Where are all these people going wrong?”. For that, we need to look at the paths they took through our tree.

Next: Where they went