AtlasSession 4L12: Introduction to measurement errors and diagnostic test accuracy studiesp.36–39
Bland–Altman and ICC
- 3 earlier topics
- Types of distribution
- Normal vs non-normal
- Graphs for quantitative data
- Scatter plots and correlation
- Bland–Altman and ICC
Fig. 1
Diabetic foot ulcer area by 3D wound camera vs acetate tracing in 60 ulcers (cm²)
Fig. 1: 60 ulcers measured by 3D camera and by acetate tracing. Each dot is one ulcer: the gap (3D camera minus acetate tracing) against its average size. 60 of 60 gaps sit inside the band.
- 3D camera reads
- about 0.8 cm² more
- Gaps inside the band
- 60 of 60
- Rise and fall together?
- yes, closely
Agreement & Error Lab · First look
Level 1 · First look · Lecture 12 · p.36–39
Explain why two methods that rise and fall together can still disagree, and how plotting the gaps shows it.
Assess agreement between two quantitative measurements with a Bland–Altman plot, explain why correlation is not agreement, and use SD and relative SD.
Two bathroom scales (the step you are on)
One always reads 1 kg more; they rise together but never agree.
Two bathroom scales: one always reads 1 kg more. Weigh yourself on both all week and they rise and fall together, yet they never agree.