The document discusses the number of participants needed to perform a reliable visual analysis of a design. It shows that using samples of 8 or 15 people can produce misleading results due to large variations in visual attention across samples. Using samples of 30 people or more produces more consistent results and is therefore recommended for a reliable visual analysis.

1. The f ollowing slides show how many participants are needed to get a reliable visual analysis of one design

2. 1 Person

3. Large improvements in data quality 2

4. Large improvements in data quality 3

5. Large improvements in data quality 4

6. Large improvements in data quality 5

7. Large improvements in data quality 8

8. Large improvements in data quality 10

9. Large improvements in data quality 12

10. Large improvements in data quality 15

11. Moderate improvements in data quality 17

12. Moderate improvements in data quality 20

13. Moderate improvements in data quality 22

14. Moderate improvements in data quality 25

15. Moderate improvements in data quality 27

16. Moderate improvements in data quality 30

17. Moderate improvements in data quality 32

18. Small improvements in data quality 35

19. Small improvements in data quality 37

20. Small improvements in data quality 40

21. Small improvements in data quality 42

22. Small improvements in data quality 45

23. Small improvements in data quality 47

24. Small improvements in data quality 53

25. Some claim 8 people are enough to analyze visual attention. Following slides show random sets of 8 people from the same study shown on previous slides.

26. 8 people Sample A

27. 8 people Sample B

28. 8 people Sample C

29. 8 people Sample D

30. 8 people Sample E

31. Heatmaps of random 8 people out of all 53 participants were very different. It means sample of 8 can give a very misleading picture of true visual attention.

32. Others claim 15 people are enough for visual analysis. How about that?

33. 15 people Sample A

34. 15 people Sample B

35. 15 people Sample C

36. 15 people Sample D

37. Variation is still too large for samples of 15 people. What about samples of 30?

38. 30 people Sample A

39. 30 people Sample B

40. CONCLUSION Reliable visual analysis demands samples larger than 30 people