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Card SortingCritical Incident TechniqueAffinity Diagramming[Working: Stub for methods]

Card sorting

Alternative names for this method: Content grouping, clustering


This is a method for discovering the latent structure in an unsorted list of statements or ideas. The investigator writes each statement on a small index card and requests six or more informants to sort these cards into groups or clusters, working on their own. The results of the individual sorts are then combined and if necessary analysed statistically.

Expected benefits

If the informants are representative of the user population for whom the application is being designed, then the result will reflect the structure in which the users expect the ideas or concepts should be presented.

When is it applicable?

This is a method for use early in the planning of an application or site, or when a site is being re-designed to meet changing needs of visitors.

What training, equipment, licences do you need to have?

Although there are computer programs and web sites available that will help you automate the process, the basic requirement is for a pack of blank index cards, and a table to seat your respondent at. The procedure is best carried out in a quiet room.

Description of method

Planning beforehand

Collect the statements you wish to analyse. Write each statement on a separate card. If your statements already exist in computer format, print them out on labels and stick the labels on index cards. Number the cards uniquely on the back.

If you have pre-defined categories into which you want the statements sorted, prepare 'place mats' on which your informants may place the cards. Otherwise ensure there is a large empty table for the informant to place their piles of cards on.

Recruit informants who will be typical of the user population for whose benefit you are preparing the analysis. It is useful to have at least six such informants.

Running the method

Shuffle the card deck so that all the informants don't get the same sequence of cards or worse, that each informant gets the previous informant's sequence. The informants receive the stack of cards, and then sort them into piles on the table in front of them, using place mats if desired. You may give a rough indication of the number of piles of cards you will expect to see, to give the informants a common understanding of the expected grain of analysis.

Explain that there may well be an 'unsortable' pile, but that they should attempt to place as many cards together into piles as they reasonably can.

Informants may attempt to show the relationship between piles of cards by spatial proximity on the table: ensure you note this information down: in the classic analytic technique, this information may get lost.

At the end, note which cards have been put together by the respondent by noting the numbers on the back of the cards. If you have not supplied place mats, invite the users to give a name to each pile of cards ("how would you describe the cards in this pile?")

Analysing the outputs

If your clusters are relatively clear and straightforward, you may simply summarise the cards which are usually placed in each pile and give an overall name for the cluster. However, the result of card sorting is not always so straightforward.

If you notice that there is not much agreement on some clusters or items, then don't do complicated statistics, but run more informants. If you had pre-defined categories, you may wish to experiment by encouraging your respondents to create their own categories in addition to yours.

The most common method of analysis for complex data from card sorting is a statistical method called cluster analysis. There are two main approaches to cluster analysis for this kind of material: linkage and hierarchical. See Lorr (1983) for further details. In order to prepare for both types of analysis, construct a similarity matrix. If there are n cards, the matrix is n x n symmetric. Most methods require the upper and lower quadrants to be filled redundantly, and for the diagonals to be filled with 1.00. In each of the cells, compute the probability p of the cards denoted by the two common co-ordinates being together: that is, if two cards x and y were sorted into the same pile q times and there are m respondents altogether, p = q / m

Some cluster analysis methods may require an index of dissimilarity, so compute p' = 1 - p and put 0.00 in the diagonals.

Reporting the results

Remember that the result of this method should be a clear indication of how the items of interest are clustered in the minds of the respondents.

Variants on the above

The most commonly used variant is these days to use computer supported methods (see below). However, some people have run this as a group exercise, with a number of informants placing stick-its on a wall or large sheet of paper (so that connections between clusters can be drawn).

Quality control

The informants should be familiar with the terms used and what the labels represent in the web site or application, and they should be end-users or visitors, not personnel involved in the technical development because this method can misfire to produce a logical or commercially-orientated grouping which does not represent the way the actual visitors see the site.

What next?

After card sorting you should proceed to design activities such as creating a (paper)prototype of the structure of the material you have been investigating. However, you may also wish to run a focus group or a brain storming session to further refine and to expand or enlarge on the results you have so far obtained.

More information

In print


Computer supported methods for card sorting may be found at:

See also information on the Infodesign page:

Case studies


Other methods that could be used instead

The nearest alternative is the affinity diagram or concept wall technique. This latter has the merit that a hierarchical arrangement can be deduced without recourse to mathematics.

History of this page and contributors

This version is adapted from the UsabilityNET web site by jk, 03-09-2018

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