Which of the following statements is FALSE for Plaque Index?

PLAQUE INDEX (PlI): The Plaque Index was described by Silness P and Loe H. in 1964 and more fully described by Loe H. in 1967.  The Plaque Index is unique among the indices used for assessment of plaque because it ignores the coronal extent of plaque on the tooth surface area and assesses only the thickness of plaque at the gingival area of the tooth. This index is one of the most widely used and has demonstrated good validity and reliability. It can be used as a full mouth index or as a simplified index.