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Card Sorting

Definition

Card sorting is a user research method used to discover how people understand and categorize information. In a card sorting session, participants organize topics or pieces of content written on cards into groups that make sense to them. This technique helps UX designers and information architects understand users' mental models, determine logical ways to structure information, and create more intuitive navigation systems and information architectures.

Types of Card Sorting

Card sorting comes in several variations, each serving different research goals:

Open Card Sort

  • Process: Participants group cards into categories they create and name themselves
  • Use Cases: Discovering how users naturally categorize content, generating new category ideas
  • Benefits: Reveals users' mental models without imposing existing structures
  • Limitations: Can result in highly divergent groupings that are difficult to reconcile

Closed Card Sort

  • Process: Participants sort cards into predefined categories
  • Use Cases: Testing or validating an existing or proposed structure
  • Benefits: More structured results that are easier to analyze quantitatively
  • Limitations: May miss opportunities for new organizational approaches

Hybrid Card Sort

  • Process: Participants sort cards into some predefined categories, but can also create their own
  • Use Cases: Validating existing categories while allowing for new discoveries
  • Benefits: Combines structure with flexibility
  • Limitations: More complex to analyze than purely open or closed sorts

Tree Testing (Reverse Card Sort)

  • Process: Tests existing hierarchy by asking participants to find items in a text-based site structure
  • Use Cases: Validating navigation and information architecture after card sorting
  • Benefits: Tests actual findability within a proposed structure
  • Limitations: Doesn't generate new organizational ideas

Card Sorting Process

A typical card sorting study follows these steps:

Preparation

  1. Define Goals: Determine specific research questions to answer
  2. Select Content: Choose representative items (usually 30-70) to include on cards
  3. Recruit Participants: Find 15-20 participants who represent your target users
  4. Select Method: Choose between in-person or online, and the type of sort

Execution

  1. Introduction: Explain the process and what you expect from participants
  2. Sorting: Have participants organize cards into logical groupings
  3. Naming: Ask participants to name the categories they've created (for open sorts)
  4. Discussion: Conduct post-sort interviews about their grouping rationale

Analysis

  1. Standardization: Normalize category names and groupings
  2. Visualization: Create dendrograms, similarity matrices, or other visualizations
  3. Pattern Identification: Look for consistent grouping patterns across participants
  4. Structure Development: Use findings to inform information architecture

In-Person vs. Online Card Sorting

Card sorting can be conducted in different environments:

In-Person Card Sorting

  • Process: Physical cards arranged on a table
  • Benefits: Direct observation of behavior, immediate follow-up questions, rich qualitative data
  • Limitations: Time-consuming, geographically limited, more difficult to analyze quantitatively

Remote/Online Card Sorting

  • Process: Digital cards sorted using specialized software
  • Benefits: Larger sample sizes, automated analysis, easier quantitative analysis, geographic diversity
  • Limitations: Less qualitative insight, limited ability to observe participant thinking

Analyzing Card Sort Results

Several techniques help make sense of card sorting data:

Quantitative Analysis

  • Standardized Agreement: Percentage of participants who grouped items together
  • Similarity Matrices: Tables showing how often items were grouped together
  • Dendrograms: Tree diagrams showing hierarchical clustering of items
  • Statistical Clustering: Algorithms that identify natural groupings in the data

Qualitative Analysis

  • Category Names: Analysis of terms participants use to describe groups
  • Participant Comments: Insights from think-aloud protocols or post-sort interviews
  • Outlier Examination: Investigation of unusual or unexpected groupings
  • Mental Model Mapping: Documenting the conceptual frameworks participants use

When to Use Card Sorting

Card sorting is particularly valuable in certain situations:

  • New Product Development: Creating initial information architecture
  • Redesign Projects: Restructuring existing content organization
  • Content Audits: Understanding how to categorize inventory
  • Navigation Design: Creating intuitive menu structures
  • Terminology Testing: Finding user-friendly labels for categories
  • Cross-Cultural Research: Understanding how different audiences categorize information

Card Sorting Best Practices

To get the most value from card sorting, follow these guidelines:

  • Use Clear Language: Write card content in simple, unambiguous terms
  • Limit Card Count: Keep the number manageable (usually 30-70 items)
  • Include Diverse Users: Recruit participants from different segments of your audience
  • Combine Methods: Use card sorting alongside other research techniques
  • Iterate: Conduct multiple sorts, refining content and categories
  • Validate Results: Test the resulting structure with tree testing or usability testing
  • Consider Context: Evaluate findings in light of business goals and technical constraints

Common Card Sorting Mistakes

Several pitfalls can undermine the effectiveness of card sorting:

  • Too Many Cards: Overwhelming participants with excessive content
  • Leading Categories: In closed sorts, creating categories that bias participants
  • Small Sample Size: Drawing conclusions from too few participants
  • Ignoring Outliers: Dismissing unusual groupings that might contain valuable insights
  • Over-reliance: Making decisions based solely on card sorting without other inputs
  • Technical Content: Using jargon or terminology unfamiliar to participants
  • Rigid Implementation: Applying results without accounting for context

Tools for Card Sorting

Several tools facilitate different approaches to card sorting:

  • Physical Cards: Index cards, sticky notes for in-person sessions
  • Specialized Software: OptimalSort, UserZoom, UXtweak
  • General-Purpose Tools: Miro, Mural for digital collaboration
  • Analytical Tools: Spreadsheets, statistical software for data analysis
  • Visualization Software: Tools for creating dendrograms and similarity matrices

Relationship to Other UX Methods

Card sorting connects with several related UX research and design techniques:

  • Information Architecture: Card sorting directly informs IA development
  • Usability Testing: Validates structures developed through card sorting
  • Tree Testing: Complements card sorting by testing navigation findability
  • Content Inventory: Often precedes card sorting to identify content to include
  • Wireframing: Translates organizational insights into interface structures
  • User Personas: Helps identify different mental models across user segments

By conducting effective card sorting exercises, UX practitioners gain valuable insights into users' mental models, enabling them to create intuitive information structures that align with how users naturally think about and categorize content.

Related Terms