Which of the following is true about the Periodontal Index?

RUSSELL'S PERIODONTAL INDEX (PI)  The Periodontal Index (PI) was developed by Russell A.L. in 1956, over a trial period of ten years.  The PI was intended to estimate deeper periodontal disease by measuring the presence or absence of gingival inflammation and its severity, pocket formation, and masticatory function. This index is reported to be useful among large populations but it is only of limited use for individuals or small groups.  The PI is a composite index because it records both the reversible changes due to gingivitis and the more destructive and presumably irreversible changes brought about by deeper periodontal disease.  The most important feature of Periodontal Disease Index is measurement of the level of the periodontal attachment related to the Cemento - Enamel Junction of the teeth.