¥There are numerous
rules (see Jolliffe, 2002a, Chapter 6) based
on:
1.Size of individual variances (eigenvalues, λk)
2.Cumulative sum of variances
3.Changes in successive variances
4.Physical interpretability
5.More complicated techniques
¥Types
2 & 4 are probably most often used in geoscience,
but rules of type 5 have been suggested and 3
(gaps between eigenvalues) is also sometimes important (e.g if EOFs are to be rotated)