Comparing embedded performance validity indicators within the WAIS-IV Letter-Number sequencing subtest to Reliable Digit Span among adults referred for evaluation of attention-deficit/hyperactivity disorder

Objectives: This study investigated the Wechsler Adult Intelligence Scale-Fourth Edition Letter-Number Sequencing (LNS) subtest as an embedded performance validity indicator among adults undergoing an attention-deficit/hyperactivity disorder (ADHD) evaluation, and its potential incremental value over Reliable Digit Span (RDS). Method: This cross-sectional study comprised 543 adults who underwent neuropsychological evaluation for ADHD. Patients were divided into valid (n = 480) and invalid (n = 63) groups based on multiple criterion performance validity tests. Results: LNS total raw scores, age-corrected scaled scores, and age- and education-corrected T-scores demonstrated excellent classification accuracy (area under the curve of .84, .83, and .82, respectively). The optimal cutoff for LNS raw score (≤16), age-corrected scaled score (≤7), and age- and education-corrected T-score (≤36) yielded .51 sensitivity and .94 specificity. Slightly lower sensitivity (.40) and higher specificity (.98) was associated with a more conservative T-score cutoff of ≤33. Multivariate models incorporating both LNS and RDS improved classification accuracy (area under the curve of .86), and LNS scores explained a significant but modest proportion of variance in validity status above and beyond RDS. Chaining LNS T-score of ≤33 with RDS cutoff of ≤7 increased sensitivity to .69 while maintaining ≥.90 specificity. Conclusions: Findings provide preliminary evidence for the criterion and construct validity of LNS as an embedded validity indicator in ADHD evaluations. Practitioners are encouraged to use LNS T-score cutoff of ≤33 or ≤36 to assess the validity of obtained test data. Employing either of these LNS cutoffs with RDS may enhance the detection of invalid performance.