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Index of Accuracy (IDA) = THF × (1 – FAF), where
THF (True Hit Fraction) = [number of correctly detected target stimuli] / [total number of target stimuli]
FAF (False Alarm Fraction) = [number of stimuli incorrectly identified as targets] / [total number of nontarget stimuli]
THF provides a measure of detection sensitivity and the FAF provides a measure of response specificity (Metz 1978). The IDA yields an overall measure of performance by combining both sensitivity and specificity factors (Le et al. 1998).
Reference:
Metz, C. E. (1978). Basic principles of ROC analysis. Seminars in Nuclear Medicine, 8, 283–298.
Le, T. H., Pardo, J. V., & Hu, X. (1998). 4T-fMRI study of nonspatialshifting of selective attention: Cerebellar and parietal contributions. Journal of Neurophysiology, 79, 1535–1548.
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