BMI	Body mass index
Clavien–Dindo	Classification system for postoperative complications
COPD	Chronic obstructive pulmonary disease
FRAIL Scale	Screening instrument for the assessment of frailty
G8	Geriatric eight (screening instrument for the assessment of frailty)
HNC	Head and neck cancer
HNSCC	Head and neck squamous cell carcinoma
IBM	International Business Machines Corporation
n	Sample size
NPV	Negative predictive value
p	p value
PPV	Positive predictive value
ROC	Receiver operating characteristic (used to assess the accuracy of tests in predictive models)
SD	Standard deviation
SPSS	Statistical package for the Social Sciences
φ	Cramer’s phi (measure of effect size in χ² test)