However, the results of the follow-up analysis were not consistent with that of the original analysis for digit span forward.
An analysis of the Digit Span subtest found that lower scores were significantly predicted by higher SCQ scores, a finding that persisted after adjusting for covariates.
Chi-square and Fisher's exact test, as appropriate, were applied for comparison of infection, morbidity and low performance in digit span test proportions between different groups in the main analysis and the attrition analysis.
However, IQ was not included as a covariate in the analysis of the WISC-IV Digit Span subtest in view of it being a component of full-scale IQ.
Cortical areas associated with digit span were identified by using a multiple-regression analysis that allowed us to focus on auditory short-term memory capacity while controlling for co-occurring deficits in single word speech perception, comprehension and production.
The Verbal fluency test provided a measure of executive function [31].The g factor was calculated via principal components analysis of the following Wechsler tests: Backward digit span, Letter-number sequencing, Matrix reasoning, Block design, Digit Symbol and Symbol Search subtests.
None of the predictors used in the basic univariate comparison and the more sophisticated GEE regression analysis showed any significant association with improved digit span test performance.
Since the Digit Span subtest was correlated with hair Hg, we conducted a post hoc analysis to determine if simple attention (as measured by Digits Forward] or more complex attention and concentration (Digits Reverse) explained the findings.
A confirmatory factor analysis of the WAIS-IV (model 5) revealed the Digit Span subtest loaded onto the Working Memory factor.76, suggesting the internal structure of the test captures the content area reasonably well.
Neuropsychological tests included in that analysis were phonemic and category fluency, Letter-Number Sequencing, Digit Span Backward, Self-Ordered Pointing, the Number-Letter task, a modified Flanker task, the Trail Making test, the Digit-Symbol test, the Face-Name Associative Memory Examination, the Six-Trial Selective Reminding test, and the Memory Capacity test.
