Fig. 4.

Definitions of true and false positives and negatives. Definitions of true and false positives and negatives after condensing six-by-six tables into two-by-two contingency tables for comparisons (a–d). In a, positive and negative results of index test (fine needle aspiration biopsy [FNAB]) separated into non-benign and benign. In b, positive results of FNAB including follicular neoplasm, suspicious for malignancy and malignant, and negative results of FNAB including benign and atypia/follicular lesion. In c, positive results of FNAB including suspicious for malignancy and malignant, and negative results of FNAB including benign, atypia/follicular lesion and follicular neoplasm. In d, positive results of FNAB including malignant only, and negative results of FNAB including benign, atypia/follicular lesion, follicular neoplasm and suspicious for malignancy. In all comparisons, positive and negative results of gold standard reference test (surgical histopathology) separated into malignant and non-malignant. Positive and negative results of surrogate reference test (clinical follow-up) and losses to follow-up separated into final diagnoses based on FNAB results. Non-diagnostic biopsies were removed from analysis as final diagnosis of malignant or non-malignant disease unclear in patients lost to follow-up. TN true negative, FN false negative, FP false positive, TP true positive, FNAB fine needle aspiration biopsy