Demographic information, DRS total and scale scores, and the total number of words generated in the one and two- minute letter fluency conditions were summarized in . The cognitive impairment group had a mean DRS total score of 118.3, indicating a relatively mild level of cognitive dysfunction. The mean DRS total score for the control group (134.4) was well above the recommended DRS cut score for dementia. As expected, significant group differences were noted on the DRS total and scale scores (excluding the attention scale) and on the letter fluency measures.
Associations between the letter fluency measures and cognitive function, as assessed by the DRS, were examined via Pearson correlations and scatter plot analyses.
Inspection of and and suggests that the association between the DRS total score and letter fluency was higher and less variable when performance on the latter was extended to two minutes. Examining the correlations between letter fluency and the DRS scale scores revealed a similar trend in that the magnitude of the correlations appeared to be descriptively higher in the two-minute condition. The DRS conceptualization scale correlated only with the number of words generated in the two- minute interval and in the second minute alone. The DRS memory scale correlated only with the number of words generated during the second minute of the letter fluency test.
Correlations between letter fluency measures, DRS scores, age and education
The total number of words generated in one minute in the Letter Fluency test plotted against the Dementia Rating Scale (DRS) total score.
The total number of words generated in two minutes in the Letter Fluency test plotted against the Dementia Rating Scale (DRS) total score.
As hypothesized, the ANOVA adjusting for the level of education showed that the control group generated significantly more words in the second minute [(M = 5.47(3.3)] compared to the cognitive impairment group [(M = 2.5(1.8)], 1F(4,55) = 4.958, p = 0.002.
The first discriminant function, which used words generated only within the first minute of administration as a predictor of group membership, was statistically significant [Λ (1) = 0.895, p = 0.011]. Overall, classification accuracy was 68.3%. Only 5 of the 20 (25%) cognitively impaired participants and 36 of the 40 (90%) control participants were correctly classified.
The second discriminant function used the total number of words generated in the two-minute letter fluency task as a predictor of group membership. This discriminant function was also statistically significant [Λ (1) = 0.826, p = 0.001]. The overall classification accuracy increased to 77%, with 11 of the 20 (55%) cognitively impaired participants and 35 of the 40 (87.5%) normal controls classified into their respective groups.