The similarity matrix helps you identify strong card pairings and potential groupings in your open and hybrid card sorts. It gives you a quick insight into the cards your participants paired together in the same group the most often. The darker the blue where two cards intersect, the more often they were paired together by your participants.

It also clusters related pair combinations together: the strongest pair is grouped next to the second-strongest pair that either of the first cards have, and so on. The algorithm (similar to the best merge method Dendrogram algorithm) attempts to cluster the similar cards down the right edge. Clusters are presented in the same shade of blue.

You could use the similarity matrix to:

To explore the similarity matrix, hover over any square to highlight the two cards and see the exact number of participants who paired them together.

The matrix below shows a number of strong clusters along the right edge, which tells us many people agreed about which cards belong together. A glance tells us this immediately, before we’ve even looked at the detail:

When we look more closely, we can find out which cards are paired together the most often:

And which cards are rarely paired together rarely, if at all:

With agreement levels like the ones in the darkest blue clusters, one option for us is to draft a set of categories based on these. And although this isn’t an exact science, we found this draft incredibly useful: