There are multiple definitions:

1. flap viability index(English)

   • the maximum weight of tissue that a single perforator can perfuse remains an important question in reconstructive microsurgery. This index refers to an empirically based equation, and has been established to determine what weight of tissue will survive on one or more perforators
   • Surgery
   • https://doi.org…000000000000191

2. fat volume index(English)

   • body mass index (BMI) and sarcopenia status are well-established prognostic factors in patients with lung cancer
   • BMI, NSCLC, OS
   • Prognosis, Oncology
   • https://doi.org…diol.2021210576

3. face validity index(English)

   • refers to assessment of perception, attitude, and practice of primary care practitioners towards allergic rhinitis practice guidelines
   • ORL, PCP, S-CVI, ARIA, CVI, EAR, EFA, GINA, IRT, KMO
   • Questionnaire, Guidelines, Family physician
   • https://doi.org…jou.2020.100482