Bimanual dexterity assessment: validation of a revised form of the turning subtest from the Minnesota Dexterity Test

Abstract

Bimanual coordination underlies many daily activities. It is tested by various versions of the old Minnesota Dexterity Test (dating back to 1931, 'turning' subtest). This, however, is ill standardized, may be time-consuming, and has poor normative data. A timed-revised form of the turning subtest (MTTrf) is presented. Age-related norms and test-retest reliability were computed. Sixty-four healthy individuals, 24-79 years, comprising 34 women, were required to pick up 60 small plastic disks from wells, rotate each disk, and transfer it to the other hand, which must replace it, as quickly as possible. Two trials were requested for each hand (ABBA sequence). The average time (seconds) across the 4 trials gave the test score. Participants were grouped (CART algorithm) into 3 statistically distinct (P<0.05) age×score strata, with cutoff 53+ and 73+ years, and tested at baseline and after 1 week. Test-retest reliability was measured both as consistency [intraclass correlation coefficient (ICCs) model 2.1] and as agreement (Bland-Altman plot). From the ICCs, the individual test-retest minimal real difference (in seconds) was computed. The whole MTTrf took less than 4 min to administer. Baseline scores ranged from 40 to 78 s. The ICCs ranged from 0.45 to 0.81 and the minimal real difference ranged from 6.68 to 13.40 s across the age groups. Fifty-nine out of 64 observations (92%) fell within the confidence limits of the Bland-Altman plot. The MTTrf is a reliable and practical test of bimanual coordination. It may be a useful addition to protocols of manual testing in occupational therapy.

Figures

Fig. 1

Sketch of the MTTrf (modified from the CMDT battery): (a) general setup; sequence of manipulations; (b) pick-up phase. Initially, the red side of the disk faces upward (here it is white); (c) transfer between hands; (d) turning and (e) replacement; later the black side of the disk faces upward (in the Figure also it is black). CMDT, Complete Minnesota Dexterity Test; MTTrf, timed-revised form of Minnesota turning test.

Fig. 2

Time in seconds to complete the MTTrf (on the ordinate) at baseline (left box in each pair) and on retest, 1 week apart (right box in each pair), as a function of age group (on the abscissa). For each participant, the completion time is given as the average of four runs, two per each beginning hand (ABBA sequence). Each box spans from the 10th to the 90th percentile of the distribution. The internal horizontal segment gives the median. The upper and lower ‘whiskers’ are extended to the minimum and the maximum observed values, respectively. See Table 1 for mean and SD. MTTrf, revised form of Minnesota turning test.

Fig. 3

Bland–Altman reliability plot of the MTTrf, performed at baseline and at 1-week retest. The ordinate gives the baseline–retest difference (in seconds). The abscissa provides the average results between the two time points. The intermediate horizontal line marks the average difference, and the upper and lower dashed lines mark the 95% confidence limits. Pitman’s test of difference in variance: r=0.066, n=64, P=0.602. MTTrf, revised form of Minnesota turning test.