Table 2.
Longitudinal Analysis:
| Dominant Hand Condition Least Squares Means | Alternating-Thumbs Condition Least Squares Means | ||||||
|---|---|---|---|---|---|---|---|
| Group | Estimate | Standard Error | Effect Size | Group | Estimate | Standard Error | Effect Size |
| NC | *0.95 | *0.36 | 0.25 | NC | *0.60 | *0.24 | 0.22 |
| Pr-HD Far | *0.25 | *0.28 | 0.07 | Pr-HD Far | *0.25 | *0.19 | 0.09 |
| Pr-HD Mid | *−0.08 | *0.26 | −0.02 | Pr-HD Mid | *−0.57 | *0.17 | −0.21 |
| Pr-HD Near | *−0.63 | *0.29 | −0.17 | Pr-HD Near | *−0.70 | *0.20 | −0.26 |
| HD Diagnosed | *−0.75 | *0.36 | −0.20 | HD Diagnosed | *−0.92 | *0.24 | −0.34 |
All Estimates and Standard Errors × 10−3
Note: In Dominant Hand condition, Group F(4,424) = 4.25, p < .01. Trend test excluding NC participants F = 6.15, p = .01. In Alternating-Thumbs Condition, Group F = 8.79, p = <.0001. Trend test excluding NC participants F(1,359) = 14.31, p < .001. Analyses comparing groups reveals a significant performance difference in NC participants compared to pr-HD mid, pr-HD near, and HD diagnosed groups, though comparisons do not significantly differ from pr-HD far group. Effect of collecting data at various sites is non-significant and so is not included in the model. Model controls for baseline age, gender, education, music and typing experience. Groups defined based on Langbehn (2004) formula using CAG repeat length and current age to estimate proximity to diagnosis as follows: pr-HD far from diagnosis = 15+ years, pr-HD midway from diagnosis = 9–15 years, pr-HD near to diagnosis = <9 years. Age and education measured in years. Music experience defined as “extensive musical training or performance experience,” typing experience defined as “experience as a typist.” Model outcome variable is mean annual change in precision, where precision is modeled as reciprocal of standard deviation of mean inter-tap interval on the self-paced timing tasks. Effect size reflects longitudinal change based on adjusted mean annual change.