Page 9 - Jolliffe I. Principal Component Analysis

Preface to the Second Edition
viii
A much shorter book on PCA (Dunteman, 1989), which is targeted at
social scientists, has also appeared since 1986. Like the slim volume by
Daultrey (1976), written mainly for geographers, it contains little technical
material.
The preface to the first edition noted some variations in terminology.
Likewise, the notation used in the literature on PCA varies quite widely.
Appendix D of Jackson (1991) provides a useful table of notation for some of
the main quantities in PCA collected from 34 references (mainly textbooks
on multivariate analysis). Where possible, the current book uses notation
adopted by a majority of authors where a consensus exists.
To end this Preface, I include a slightly frivolous, but nevertheless in-
teresting, aside on both the increasing popularity of PCA and on its
terminology. It was noted in the preface to the first edition that both
terms ‘principal component analysis’ and ‘principal components analysis’
are widely used. I have always preferred the singular form as it is compati-
ble with ‘factor analysis,’ ‘cluster analysis,’ ‘canonical correlation analysis’
and so on, but had no clear idea whether the singular or plural form was
more frequently used. A search for references to the two forms in key words
or titles of articles using the Web of Science for the six years 1995–2000, re-
vealed that the number of singular to plural occurrences were, respectively,
1017 to 527 in 1995–1996; 1330 to 620 in 1997–1998; and 1634 to 635 in
1999–2000. Thus, there has been nearly a 50 percent increase in citations
of PCA in one form or another in that period, but most of that increase
has been in the singular form, which now accounts for 72% of occurrences.
Happily, it is not necessary to change the title of this book.

I. T. Jolliffe
April, 2002
Aberdeen, U. K.