Pitfalls of using IQ short forms in neurodevelopmental disorders: a study in patients with congenital heart disease

Ehrler M, Latal B, Polentarutti S, von Rhein M, Held L, Wehrle FM.

Pediatr Res. 2020 Apr;87(5):917-923. doi: 10.1038/s41390-019-0667-2. Epub 2019 Nov 11.

PMID: 31711070

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Background: Short forms of IQ (S-IQ) assessments are time efficient and highly predictive of the full IQ (F-IQ) in healthy individuals. To investigate the validity of S-IQs for patients with neurodevelopmental impairments, this study tested a well-established S-IQ version in patients with congenital heart disease (CHD).

Methods: The Wechsler Intelligence Scale for Children, Fourth Edition was applied in 107 children with complex CHD aged 9-11 years. F-IQ and a well-established S-IQ version were calculated for each patient. The agreement between S-IQ and F-IQ was investigated across the whole spectrum of IQ scores. Finally, we tested a method to adjust IQs to resolve potential bias and validated this method in an independent sample of 55 CHD patients.

Results: S-IQ and F-IQ correlated strongly. Nevertheless, the size of the bias correlated with the true IQ, indicating larger error at the tails of the distribution. Estimating a corrected IQ by adjusting the S-IQ with correction parameters substantially improved agreement.

Conclusion: We here report that substantial bias may underestimate low IQ scores and overestimate high ones. This bias should be considered when at-risk populations are assessed with S-IQs. Importantly, the bias can be minimized by using a correction formula.