Resumen: Several approaches and descriptors have been proposed to characterize the purity of coherency or density matrices describing physical states, including the polarimetric purity of 2D and 3D partially polarized waves. This work introduces two interpretations of the degree of purity: one derived from statistics and another from algebra. In the first one, the degree purity is expressed in terms of the mean and standard deviation of the eigenvalue spectrum of the density or coherency matrix of the corresponding state. The second one expresses the purity in terms of two specific measures obtained by decomposing the coherency matrix as a sum of traceless symmetric, antisymmetric, and scalar matrices. We believe these two approaches offer better insights into the purity measure. Furthermore, interesting relations with existing quantities in polarization optics also are described. Idioma: Inglés DOI: 10.1364/JOSAA.476423 Año: 2022 Publicado en: Journal of the Optical Society of America. A, Optics, image science, and vision 39, 12 (2022), 2339-2342 ISSN: 1084-7529 Factor impacto JCR: 1.9 (2022) Categ. JCR: OPTICS rank: 68 / 99 = 0.687 (2022) - Q3 - T3 Factor impacto CITESCORE: 4.0 - Materials Science (Q2) - Computer Science (Q2) - Physics and Astronomy (Q2)