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Learn through experiments

Fast for whom?

Can a faster average conceal a design failure?

Entering midway? Revisit Prototype and repair a navigation flow for the preceding worked example, or start here and use the explanation below.

1 · Try

Start with a concrete question

Four authored task observations compare a pointer-only menu, a basic accessible revision and a streamlined revision. These fixtures are not real usability study data.

Try the initial inputs, then write a prediction before changing one setting. All calculations run locally on your CPU.

Go directly to the experiment · Review basic mathematics

2 · Predict

What do you expect?

Predict why the pointer-only design can look fast when blocked tasks are omitted.

3 · Experiment

Change one thing. Inspect what happens.

  1. Inspect all tasks for the pointer-only design; count blocked tasks before reading timing.
  2. Filter to keyboard tasks and interpret the undefined mean.
  3. Compare revisions separately for keyboard and touch.
  4. Write an acceptance rule that includes success and timing; explain what this tiny fixture cannot prove.
Experiment inputs
Inputs
Your settingsMechanism
Calculation belowEvidence
Compare outcomes
Successful tasks2 of 4
Time on successful tasks28 seconds
Mean successful task time14 seconds

Compare the current results

Every bar starts at zero and uses the same numeric scale in this chart. The upper bound automatically adjusts to the largest current value (at least 1), so compare the numbers when changing inputs. Units and quantities come from each label; different kinds of quantity are not interchangeable. Displayed values are rounded to at most six significant digits.
02
  • Successful tasks2
    Successful tasks: 2Horizontal bar from zero to 2, on the shared zero to 2 numeric axis.
  • Blocked tasks2
    Blocked tasks: 2Horizontal bar from zero to 2, on the shared zero to 2 numeric axis.

Follow the calculation

  1. Keyboard: open menu: blocked; omitted from successful-task timing.
  2. Keyboard: submit form: blocked; omitted from successful-task timing.
  3. Touch: open menu: 8 seconds, completed.
  4. Touch: submit form: 20 seconds, completed.
  5. Compare success counts before comparing average times. Zero represents a blocked task in the fixture, never instantaneous success.

A fast average among successful attempts can hide excluded users. Inspect the keyboard and touch groups separately.

Captures keep your inputs, prediction and observation. Results are recalculated from those inputs. Resetting inputs keeps your captures and challenge history.

4 · Understand

Explain the mechanism

Fast for whom?

Four authored task observations compare a pointer-only menu, a basic accessible revision and a streamlined revision. These fixtures are not real usability study data.

Follow the mechanism

Timing only successful tasks changes who is represented. A design that blocks two tasks must not receive credit for doing them quickly.

The basic revision completes all four tasks in 69 seconds total. The pointer-only design totals 28 seconds, but only for two successful touch tasks.

Group inspection reveals exclusions that a single average can hide. Real accessibility evaluation also needs broader tasks, tools and human testing.

Worked example

Keyboard: open menu: blocked; omitted from successful-task timing.

Keyboard: submit form: blocked; omitted from successful-task timing.

Touch: open menu: 8 seconds, completed.

Touch: submit form: 20 seconds, completed.

Compare success counts before comparing average times. Zero represents a blocked task in the fixture, never instantaneous success.

Calculation

Mean successful task time = total successful time ÷ number of successful tasks; undefined when there are none.

Try a controlled comparison

  1. Inspect all tasks for the pointer-only design; count blocked tasks before reading timing.

  2. Filter to keyboard tasks and interpret the undefined mean.

  3. Compare revisions separately for keyboard and touch.

  4. Write an acceptance rule that includes success and timing; explain what this tiny fixture cannot prove.

What this does not establish

  • Observations are deterministic authored examples, not measured performance.

  • Passing these four cases is not accessibility certification or evidence of universal usability.

5 · Apply

Try a fresh case

A new prototype completes three tasks in 12, 18 and 24 seconds and blocks one other task. What is its mean successful-task time in seconds?

This is a public practice check. Retries support learning; matching a number does not certify independent proficiency.

Take the investigation further

Choose any extension. These are project prompts for you to carry out; they are not automatically assessed.

School investigation

Test a paper prototype with two classmates using a clear task script.

College investigation

Design a study that includes assistive-technology users and explicit task failures.

Workplace investigation

Create a release checklist linking observed exclusions to repairs and follow-up testing.

6 · Continue

Keep the evidence, choose your next step

Completion records your own decision that you have worked through this investigation. Practice checks and independent project evidence are separate.