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. Author manuscript; available in PMC: 2015 Jan 1.
Published in final edited form as: Neuropsychologia. 2013 Nov 21;53:137–145. doi: 10.1016/j.neuropsychologia.2013.11.008

Table 3.

Regression type, beta coefficients, and corresponding p-values for each model examining Processing Speed Index (PSI) as a function of whole brain fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD), after controlling for age and group status. Because of head coil changes in the DTI data collection, Time 1 and Time 3 were examined together (using a longitudinal linear mixed-effects model) and then separately (using separate linear regressions).

PSI~ Intercept+ Whole Brain FA + Group + Age + Whole Brain FA*Group
Regression Type Intercept p-value Whole Brain FA p-value Group p-value Age p-value Whole Brain FA X Group p-value
Time 1 & Time 3 Linear Mixed-Effects −22.25 .71 256.69 .04 87.67 .19 −0.04 .82 −210.05 .12
Time 1 Linear 3.77 .97 205.00 .36 1.95 .99 0.09 .83 −41.74 .88
Time 3 Linear −29.59 .71 274.17 .09 139.88 .15 −0.15 .42 −310.03 .10
PSI~ Intercept+ Whole Brain MD+ Group + Age + Whole Brain MD*Group
Regression Type Intercept p-value Whole Brain MD p-value Group p-value Age p-value Whole Brain MD X Group p-value
Time 1 & Time 3 Linear Mixed-Effects 178.88 <.001 −86.91 .24 −70.22 .29 0.03 .87 63.12 .43
Time 1 Linear 43.10 .80 72.07 .71 127.45 .48 0.24 .57 −174.48 .41
Time 3 Linear 204.67 .02 −117.43 .27 −118.47 .22 −0.11 .56 123.51 .29
PSI~ Intercept+ Whole Brain RD+ Group + Age + Whole Brain RD*Group
Regression Type Intercept p-value Whole Brain RD p-value Group p-value Age p-value Whole Brain RD X Group p-value
Time 1 & Time 3 Linear Mixed-Effects 176.02 <.001 −118.84 .11 −73.44 .11 0.01 .95 95.54 .23
Time 1 Linear 120. 48 .25 −28.06 .87 18.90 .86 0.21 .63 −63.01 .74
Time 3 Linear 187. 43 <.00 −136.88 .16 −99.43 .11 −0.12 .50 143.03 .19
PSI~ Intercept+ Whole Brain AD+ Group + Age + Whole Brain AD*Group
Regression Type Intercept p-value Whole Brain AD p-value Group p-value Age p-value Whole Brain AD X Group p-value
Time 1 & Time 3 Linear Mixed-Effects 122.33 .12 −11.28 .85 −9.43 .92 0.06 .71 −6.99 .92
Time 1 Linear −128.65 .52 175.96 .25 327. 94 .18 0.15 .71 −261.33 .15
Time 3 Linear 143.17 .23 −26.62 .77 −58.09 .68 −0.08 .66 30.86 .77