← VCE Data Analytics U3O2

Judging efficiency and effectiveness of a data visualisation

Effective = viewers answer the research question correctly. Efficient = they answer quickly, with little effort. Back each judgement with evidence, like test times.

Part of: VCE Data Analytics - U3O2 - Analysis and Design — Module 144

Understanding Judging efficiency and effectiveness of a data visualisation in VCE Data Analytics U3O2

What it does: Recorded times are measurable evidence that supports a judgement about how efficient a visualisation is. Effectiveness is about correct answers. Speed and effort relate to efficiency. Correct answers make it effective, but two minutes is slow, so it is not efficient. Extra steps and effort reduce efficiency, even if viewers still get the right answer.

Common mistakes: Effectiveness is the share of viewers who answered correctly out of everyone tested. Setting total to correct makes the rate always 100%. It should be total ← 20. Efficiency is judged by the time viewers take, so each test time must be added to the total. Adding 1 only counts viewers. It should be sum ← sum + t.

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Learning
Duo
A visualisation is effective if viewers can...
Answer the research question correctlyAnswer the research question quickly
Matches
All 5 testers answered correctly, so the dashboard is efficient.
↓
Correct answers show effectiveness, not efficiency. Efficiency needs evidence about time or effort, such as how many seconds testers took.
Applying
Meanings
Term
effectiveness and efficiency
Meaning
Effective = viewers answer the research question correctly. Efficient = they answer quickly, with little effort. Back each judgement with evidence, like test times.
Practice
Viewers tested: 5
Testing
Gaps
=(B2:B9)
Check Answer
Spots
1correct ← 18
2total ← correct

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Quick Questions

1. A visualisation is effective if viewers can...
A. Answer the research question quickly
B. Answer the research question correctly ✓
Effectiveness is about correct answers. Speed and effort relate to efficiency.
2. Which measure best shows efficiency?
A. The number of colours used in the chart
B. The time viewers take to find an answer ✓
Efficiency is about speed and low effort, so time to find an answer is good evidence.
3. 10 of 10 test viewers read the right value from a chart, but it took each of them over two minutes. The chart is...
A. Effective but not efficient ✓
B. Efficient but not effective
Correct answers make it effective, but two minutes is slow, so it is not efficient.
4. Viewers find the answer in 5 seconds, but 7 of 10 give the wrong answer. The chart is...
A. Efficient but not effective ✓
B. Effective but not efficient
Fast answers make it efficient, but most answers were wrong, so it is not effective.
5. Which statement is a judgement backed by evidence?
A. The dashboard is effective: 9 of 10 testers correctly named the top region ✓
B. The dashboard is effective because it looks great
Evidence such as test results supports a judgement. Opinion alone does not.

Match the Pairs

Effective visualisation → Viewers answer the research question correctly after reading the visualisation
Efficient visualisation → Viewers find the answer quickly and with little effort
Evidence for efficiency: time taken by each tester to find the answer → Tester 1: 12 seconds, Tester 2: 9 seconds, Tester 3: 15 seconds
Evidence for effectiveness: how many testers gave the correct answer → 4 of 5 testers named the correct region (80% correct)
All 5 testers answered correctly, so the dashboard is efficient. → Correct answers show effectiveness, not efficiency. Efficiency needs evidence about time or effort, such as how many seconds testers took.
Testers found the answer in 8 seconds, so the chart is effective. → Fast times show efficiency, not effectiveness. Effectiveness needs evidence that the answers were correct, which is not given.

Key Term

effectiveness and efficiency
Effective = viewers answer the research question correctly. Efficient = they answer quickly, with little effort. Back each judgement with evidence, like test times.

Fill in the Blanks

1. =AVERAGE(B2:B9)
Hint: Type the function that finds the mean time viewers took to find an answer (a measure of efficiency).
2. =COUNTIF(C2:C9,"Correct")
Hint: Type the function that counts only the viewers who answered correctly (evidence of effectiveness).
3. =COUNTIF(C2:C9,"Correct")/COUNTA(C2:C9)
Hint: Type the function that counts every response, so the number of correct answers becomes a proportion.
4. =MAX(B2:B9)
Hint: Type the function that finds the slowest time in the test, showing the worst case for efficiency.
5. IF avgTime <= 10 THEN verdict ← "Efficient" END IF
Hint: Type the comparison operator meaning the average time is at most the target, because quicker is more efficient.

Spot the Error

Question 1
A correct ← 18
B total ← correct
C rate ← correct / total * 100
D PRINT rate
Line B — Effectiveness is the share of viewers who answered correctly out of everyone tested. Setting total to correct makes the rate always 100%. It should be total ← 20.
Question 2
A times ← [12, 9, 15, 8]
B sum ← 0
C FOR EACH t IN times
D sum ← sum + 1
E END FOR
F avg ← sum / LENGTH(times)
Line D — Efficiency is judged by the time viewers take, so each test time must be added to the total. Adding 1 only counts viewers. It should be sum ← sum + t.
Question 3
A avgTime ← 8
B IF avgTime >= 10 THEN
C PRINT "Efficient"
D END IF
Line B — A visualisation is efficient when viewers find answers quickly, so the average time must be at or below the target. It should be IF avgTime <= 10 THEN.
Question 4
A IF correctRate >= 80 THEN
B verdict ← "Efficient"
C ELSE
D verdict ← "Not effective"
Line B — A high rate of correct answers shows the visualisation is effective, not efficient. Efficiency is about time and effort. It should be verdict ← "Effective".
Question 5
A taken ← endTime + startTime
B PRINT taken
C IF taken < 10 THEN
D PRINT "Quick to use"
Line A — The time to find an answer is the end time minus the start time. Adding them gives a meaningless value. It should be taken ← endTime - startTime.

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