International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.8, p. 327

Figure 3.8.2 

C. J. Gilmore,a G. Barra and W. Donga*

aDepartment of Chemistry, University of Glasgow, University Avenue, Glasgow, G12 8QQ, UK
Correspondence e-mail:  chris@chem.gla.ac.uk

[Figure 3.8.2]
Figure 3.8.2

Four different methods of estimating the number of clusters present in a set of 23 powder patterns for the drug doxazosin. A total of five polymorphs are present, as well as two mixtures of these polymorphs. (a) A scree plot from the eigenvalue analysis of the correlation matrix; (b) the use of the C test (the coefficients have been multiplied by 100.0), which gives an estimate of five clusters using its local maximum. The γ test estimates that there are seven clusters and the CH test has a local maximum at seven clusters. Numerical details are given in Table 3.8.2[link].