Parkinson's disease and the Stroop color word test: processing speed and interference algorithms.

OBJECTIVE

Processing speed alters the traditional Stroop calculations of interference. Consequently, alternative algorithms for calculating Stroop interference have been introduced to control for processing speed, and have done so in a multiple sclerosis sample. This study examined how these processing speed correction algorithms change interference scores for individuals with idiopathic Parkinson's disease (PD, n = 58) and non-PD peers (n = 68).

METHOD

Linear regressions controlling for demographics predicted group (PD vs. non-PD) differences for Jensen's, Golden's, relative, ratio, and residualized interference scores. To examine convergent and divergent validity, interference scores were correlated with standardized measures of processing speed and executive function.

RESULTS

PD-non-PD differences were found for Jensen's interference score, but not Golden's score, or the relative, ratio, and residualized interference scores. Jensen's score correlated significantly with standardized processing speed but not executive function measures. Relative, ratio, and residualized scores correlated with executive function but not processing speed measures. Golden's score did not correlate with any other standardized measures.

CONCLUSIONS

The relative, ratio, and residualized scores were comparable for measuring Stroop interference in processing speed-impaired populations. Overall, the ratio interference score may be the most useful calculation method to control for processing speed in this population.