Diagnostics › Method comparison

Mountain plot (folded ECDF of differences)

A mountain plot folds the empirical CDF of paired differences (A − B) at the median — the same information as Bland-Altman, read as a peak.

What is Mountain plot (folded ECDF of differences)?

Krouwer and Monti folded the right half of the ECDF over the median so the percentile curve climbs to a peak at the median and descends symmetrically. Reading it: the peak is the median difference; the width at any height tells you what fraction of differences are inside that range.

Equivalent to a Bland-Altman plot in information content, but easier for some audiences — the 'mountain' shape conveys both centre and spread of the differences in one glance.

When should I use Mountain plot (folded ECDF of differences)?

  • Alternative visualisation of paired differences when you want a single-axis representation.
  • Reporting agreement to a non-statistical audience.

What data does it need?

Two numeric columns measuring the same quantity, paired by row.

What does it report?

Folded ECDF plot with the median difference marked.

How do I interpret the result?

A symmetric mountain centred on zero ⇒ no bias; an asymmetric mountain or one off-centre ⇒ bias whose direction matches the offset.

See also

References

  • Krouwer & Monti (1995). A simple, graphical method to evaluate laboratory assays. Eur. J. Clin. Chem. Clin. Biochem. 33(8).