Principles of UX / UI (Product Design): System Usability Scale (SUS) and SEQ

System Usability Scale (SUS) and SEQ

Portfolio-Ready Study Guide: System Usability Scale (SUS) & Single Ease Question (SEQ)

What This Is

The System Usability Scale (SUS) and Single Ease Question (SEQ) are quick, standardized ways to measure how easy (or frustrating) a product is to use. Think of them as a "usability thermometer"—they give you a single score to compare designs, track improvements, or prove to stakeholders that your changes worked.

Example: You redesign a hospital’s patient portal to let users book appointments in 3 steps instead of 7. After testing, you run a SUS survey and see the score jump from 45 (poor) to 78 (good). Now you can confidently say, "This redesign made the portal 73% more usable." SEQ, on the other hand, asks users to rate a specific task (e.g., "How easy was it to find your lab results?") on a 1–7 scale, helping you pinpoint exactly where users struggle.

Key Terms & Principles

• System Usability Scale (SUS):
  A 10-question survey (odd-numbered questions are positive, even are negative) that gives a 0–100 score of overall usability. Example: After testing a new mobile banking app, users rate statements like "I found the app unnecessarily complex" (1 = Strongly Disagree, 5 = Strongly Agree). A score >68 is "good"; >80 is "excellent."

• Single Ease Question (SEQ):
  A single question asked after a user completes a task: "Overall, how difficult or easy was this task to complete?" (1 = Very Difficult, 7 = Very Easy). Example: After a user books a flight, you ask, "How easy was it to select your seat?" Scores <5 signal problems.

• Likert Scale:
  A rating scale (e.g., 1–5 or 1–7) used in SUS and SEQ. Example: "I think I would use this website frequently" (1 = Strongly Disagree, 5 = Strongly Agree).

• Ceiling/Floor Effects:
  When scores cluster at the top (ceiling) or bottom (floor) of a scale, making it hard to measure improvement. Example: If 90% of users rate a task as "7" on SEQ, the scale isn’t sensitive enough—try a 1–10 scale instead.

• Standardization:
  Using the same questions, scale, and scoring method every time to compare results. Example: Always use the exact SUS wording (don’t change "I found the system very cumbersome" to "This was hard to use").

• Benchmarking:
  Comparing your SUS/SEQ scores to industry standards. Example: A SUS score of 70 is average for e-commerce; 80+ is elite (like Amazon).

• Task Completion Rate:
  The % of users who successfully finish a task (e.g., "80% of users booked an appointment without help"). SEQ scores often correlate with this—low SEQ = low completion.

• Heuristic Evaluation:
  A usability inspection where experts check a design against Nielsen’s 10 Usability Heuristics (e.g., "Does the system match real-world language?"). Example: If users struggle to find a "Cancel Subscription" button, it violates Visibility of System Status and User Control and Freedom.

• Guerrilla Testing:
  Quick, informal usability tests with 5–10 users (e.g., asking strangers in a café to try your prototype). Example: After a SEQ test, you notice users rate "Finding the return policy" as a 3/7, so you move the link to the footer.

• A/B Testing:
  Comparing two versions of a design to see which performs better. Example: Version A (SUS = 65) vs. Version B (SUS = 72)—you ship Version B.

• Cognitive Load:
  The mental effort required to use a product. High cognitive load = low SUS/SEQ scores. Example: A form with 20 fields will score worse than one with 5.

• Progressive Disclosure:
  Showing only the most important info first, then revealing details as needed. Example: A checkout flow that hides shipping options until the user enters their address (reduces cognitive load, improves SEQ).

Step-by-Step / Process Flow

1. Define Your Goal & Tasks

• Action: Write down what you’re testing and why.
• Example: "We redesigned the checkout flow to reduce cart abandonment. We’ll test if users can complete a purchase in <2 minutes."
• Figma Tip: Create a task script in a sticky note (e.g., "Find the blue sneakers, add to cart, check out as a guest").

2. Recruit Users (5–10 for SUS, 10–20 for SEQ)

• Action: Use guerrilla testing (friends, coworkers) or tools like UserTesting.com or Maze.
• Pro Tip: For SEQ, test at least 10 users per task to spot trends.
• Figma Tip: Use the Figma User Testing Plugin to record sessions and SEQ responses.

3. Run the Test (Moderated or Unmoderated)

• Moderated (Live):
• Give users the task (e.g., "Book a doctor’s appointment").
• Observe silently (don’t help!).
• After the task, ask SEQ: "How easy was that?" (1–7).
• At the end, give the SUS survey (10 questions).
• Unmoderated (Remote):
• Use Maze or UserZoom to set up tasks + SEQ/SUS.
• Example: "Try to find the return policy. Rate how easy it was (1–7)."
• Figma Tip: For unmoderated tests, use Figma’s Prototype Mode to link screens and record clicks.

4. Calculate Scores

• SUS Score:
• For odd questions (1,3,5,7,9), subtract 1 from the user’s score.
• For even questions (2,4,6,8,10), subtract the user’s score from 5.
• Add all scores, multiply by 2.5 → Final SUS score (0–100).
• Example: If a user scores Q1=4, Q2=2 → (4-1) + (5-2) = 3 + 3 = 6 → 6 × 2.5 = 15 (part of the total).
• SEQ Score:
• Average all user ratings (1–7). <5 = problem area.

5. Analyze & Iterate

• Action: Look for patterns.
• Low SUS (<68)? The whole experience is frustrating (e.g., slow load times, confusing IA).
• Low SEQ on one task? That specific flow is broken (e.g., users can’t find the "Submit" button).
• Figma Tip: Use Figma’s Auto-Animate to prototype fixes (e.g., moving a button) and retest.

6. Report Findings (Portfolio-Ready!)

• Action: Summarize in a 1-page case study with:
• Before/After SUS scores (e.g., "SUS improved from 52 to 78").
• SEQ task breakdown (e.g., "‘Apply promo code’ scored 3/7—users couldn’t find the field").
• Visuals: Screenshots of the old vs. new design + a bar chart of SEQ scores.
• Portfolio Tip: Add a short video clip of a user struggling (with permission) to show empathy.

Common Mistakes

Mistake 1: Changing the SUS Questions

• Why it’s bad: SUS is standardized—changing wording makes scores unreliable.
• Correction: Use the exact 10 questions from the official SUS template. Example:
• ❌ "This app was hard to use." (Too vague)
• ✅ "I found the system unnecessarily complex." (Official wording)

Mistake 2: Testing Too Few Users

• Why it’s bad: 3 users won’t give you reliable SUS/SEQ scores.
• Correction: Test at least 5 users for SUS, 10+ for SEQ (per task). Use Nielsen’s Law of Usability Testing: "5 users find 85% of problems."

Mistake 3: Leading Users During SEQ

• Why it’s bad: "That was easy, right?" biases their answer.
• Correction: Ask neutrally: "How easy or difficult was that task?" (1–7). Don’t explain the scale—let them interpret it.

Mistake 4: Ignoring Qualitative Feedback

• Why it’s bad: SUS/SEQ give numbers, but users’ comments explain why they scored low.
• Correction: Always ask "What was confusing?" after SEQ. Example: A user rates a task 2/7 and says, "I couldn’t find the ‘Next’ button." → Fix the button placement.

Mistake 5: Not Benchmarking

• Why it’s bad: A SUS score of 70 means nothing without context.
• Correction: Compare to industry averages:
• E-commerce: 70 (average), 80+ (elite)
• Healthcare portals: 60 (average), 75+ (good)
• Mobile apps: 65 (average), 80+ (great)

Design Interview / Portfolio Tips

1. Show Your Process, Not Just Scores

• Interviewers want to see: "How did you use SUS/SEQ to improve the design?"
• Portfolio Tip: Include a before/after case study with:
• Problem: "Users abandoned checkout at 60%."
• Research: "SUS score was 45; SEQ for ‘Enter payment’ was 2/7."
• Solution: "Simplified form fields, added progress bar."
• Result: "SUS improved to 78; SEQ for payment rose to 6/7."

2. Explain the "Why" Behind Scores

• Tricky Question: "Why did users rate this task a 3/7?"
• Answer: "The SEQ score was low because the ‘Submit’ button was below the fold (Jakob’s Law—users expect primary actions at the top). We moved it up, and the score jumped to 6/7."

3. Differentiate SUS vs. SEQ

• Interviewer Test: "When would you use SUS vs. SEQ?"
• Answer:
• SUS: For overall usability (e.g., "Is this app easy to use?").
• SEQ: For specific tasks (e.g., "How easy was it to reset your password?").

4. Connect to Design Principles

• Interviewer Test: "How does SUS relate to heuristics?"
• Answer: "Low SUS scores often point to heuristic violations. Example: A SUS score of 50 might mean the system violates Consistency and Standards (users don’t recognize icons) or Error Prevention (users keep entering wrong data)."

Quick Check Questions

1. A stakeholder says, "Our SUS score is 72—great! But users still complain about the checkout flow." What’s likely happening?

• Answer: The SUS score is an average—it might hide problems in specific tasks. Run SEQ on the checkout flow to pinpoint issues (e.g., "How easy was it to enter your shipping address?"). Key Principle: SUS measures overall usability; SEQ measures task-specific ease.

2. You test a new feature and get these SEQ scores: Task A = 6/7, Task B = 3/7, Task C = 5/7. What do you do next?

• Answer: Prioritize fixing Task B (lowest score). Use qualitative feedback to find the problem (e.g., "Users couldn’t find the ‘Save’ button"). Key Principle: SEQ helps identify the most critical usability issues.

3. A user rates a task 1/7 on SEQ but says, "It was fine." What’s going on?

• Answer: The user might be socially desiring (not wanting to criticize) or misunderstood the scale. Ask follow-up questions: "What was the hardest part?" or "Show me where you got stuck." Key Principle: Quantitative data (SEQ) + qualitative feedback = full picture.

Last-Minute Cram Sheet

1. SUS = 10 questions, 0–100 score. >68 = good, >80 = excellent.
2. SEQ = 1 question, 1–7 scale. <5 = problem area.
3. Always test 5+ users for SUS, 10+ for SEQ (per task).
4. Never change SUS wording—use the official template.
5. Low SUS? Check for heuristic violations (e.g., poor error messages, hidden actions).
6. Low SEQ on a task? Use guerrilla testing to observe where users struggle.
7. Benchmark SUS scores: E-commerce (70), healthcare (60), mobile apps (65).
8. ⚠️ SUS ≠ SEQ: SUS = overall usability; SEQ = task-specific ease.
9. ⚠️ Don’t lead users: Ask "How easy was that?" not "That was easy, right?"
10. Portfolio tip: Show before/after SUS/SEQ scores + user quotes to prove impact.