I have an online grocery website, it includes different categories and subcategories, I want to test the the usability of categories tree, in this case closed card sorting or open card sorting is the most suitable? and how many people should participate ?
Open or closed card sorting is the popular ones, but there is another interesting technique that put less mental load on participants, the Delphi method:
In this approach, the first participant creates an initial sort, and then the remaining participants review and modify that sort. This imposes a much lower mental load on the remaining participants, rendering a sort of 200+ items a much more tractable proposition (in theory).
It's an alternative supported by Donna Spencer who wrote the Card Sorting Book.
Reverse Card Sort
An existing structure of categories and sub-categories is tested
The reasons are:
- Open and closed card sorting techniques are used during the designing phase to understand user's mental models.
- You have already built a website with navigation structure / flow
- Now, you are trying to do the usability testing to cross check whether the items which you grouped and labelled are easy to find.
I know you have already selected the answer but wanted to post my answer.
Reference: Human Factors International (CUA - Books).
Unfortunately, I cannot share the information from the books, but here is link https://en.wikipedia.org/wiki/Card_sorting
Open or closed, are your categories defined and cannot be changed? If that is the case then a closed cardsort, if not then I would use an open sort as you will be able to see if the catergory terminology and major relationships have any underlaying issues.
If you are to use a open sort you will get alot of variation in the catergory definitions so I like to use a minimum of 12 participants, this should find the major issues with multiple particpants confirming the same issues, But if you can get, get as many as you can within your ability and scope of time.
I am not sure about free tools but optimal workshop have an online tool that i believe allows for both cardsorting options, https://www.optimalworkshop.com/optimalsort .