In this way, it mirrors other interdisciplinary fields, such as psychometrics and econometrics. Beck is noted for his research in psychotherapy, psychopathology, suicide, and psychometrics. This kind of measurement is the focus of psychometrics and psychophysics. In psychometrics and psychophysics, the term "accuracy" is interchangeably used with validity and "constant error". Construct validity is particularly important in the social sciences, psychology, psychometrics and language studies. Mathematical psychology is therefore closely related to psychometrics. The origin of psychometrics also has connections to the related field of psychophysics. PCA is also popular in psychology, especially within the field of psychometrics. The science behind psychological testing is psychometrics. Cattell soon adopted the methods of Galton and helped laying the foundation of psychometrics. Several different theories of intelligence have historically been important for psychometrics. Cattell was a strong advocate of factor analysis and psychometrics. American psychologist Zick Rubin sought to define "love" by psychometrics in the 1970s. He has also contributed to fields as diverse as computer music, psychometrics and VLSI design. The CDI manual includes comprehensive information about psychometrics, norms, and item development.