Hello!
I'm interested in running an unpaired t-test in 3dttest++ comparing functional connectivity (of amygdala ROI) between 2 groups while controlling for categorical (Site (4 levels), Maternal Education (3 levels)) and continuous (Father's Age) covariates of no-interest.
Based on
this previous post, I have noted that categorical variables with two levels should be coded as 1/-1 (or 0.5/-0.5). From the
link provided in that post, it seems like this is either "simple coding" or "deviation coding" (though the examples show 4 levels). Assuming that I should be using deviation coding, I have coded the categorical covariates numerically (please see below for my covariates file). Is this the correct way to code for categorical variables of no-interest that have more than two levels in 3dttest++? Also, is there a significant difference in the interpretation of the results when coding using 1/-1 versus 0.5/-0.5?
Thank you for your time and kind help!
-Janelle
Covariate File used with 3dttest++:
SubID Site1 Site2 Site3 MEdu1 MEdu2 FatherAge
sub01 1 0 0 0 1 42.98
sub02 1 0 0 1 0 46.89
sub03 1 0 0 1 0 41.1
sub04 1 0 0 0 1 29.87
sub05 1 0 0 0 1 34.55
sub06 1 0 0 0 1 42.13
sub07 1 0 0 1 0 43.75
sub08 1 0 0 1 0 38.45
sub09 1 0 0 1 0 37.13
sub10 1 0 0 -1 -1 24.96
sub11 0 1 0 0 1 35
sub12 0 1 0 1 0 36.06
sub13 0 1 0 -1 -1 35.31
sub14 0 1 0 -1 -1 48.19
sub15 0 1 0 1 0 41.45
sub16 0 1 0 0 1 27.88
sub17 0 1 0 1 0 35.5
sub18 0 1 0 0 1 33.16
sub19 0 1 0 0 1 30.82
sub20 0 1 0 1 0 36.34
sub21 0 1 0 0 1 32.5
sub22 0 1 0 0 1 40.05
sub23 0 1 0 0 1 34.94
sub24 0 1 0 1 0 39.59
sub25 0 1 0 0 1 37.95
sub26 0 1 0 1 0 31.81
sub27 0 1 0 1 0 31.83
sub28 0 1 0 0 1 42.19
sub29 0 1 0 -1 -1 27.43
sub30 0 1 0 1 0 32.98
sub31 0 1 0 0 1 33.7
sub32 0 0 1 0 1 45.21
sub33 0 0 1 -1 -1 44.63
sub34 0 0 1 -1 -1 39.7
sub35 0 0 1 1 0 31.62
sub36 0 0 1 0 1 48.98
sub37 0 0 1 0 1 34.7
sub38 0 0 1 -1 -1 32.14
sub39 0 0 1 0 1 27.32
sub40 0 0 1 1 0 37.04
sub41 0 0 1 1 0 39.52
sub42 0 0 1 1 0 44.05
sub43 0 0 1 1 0 35.45
sub44 0 0 1 -1 -1 30.1
sub45 0 0 1 1 0 33.77
sub46 0 0 1 -1 -1 34.82
sub47 0 0 1 -1 -1 30.81
sub48 0 0 1 1 0 41.64
sub49 0 0 1 0 1 38.17
sub50 0 0 1 1 0 38.63
sub51 -1 -1 -1 1 0 38.34
sub52 -1 -1 -1 1 0 30.44
sub53 -1 -1 -1 1 0 29.98
sub54 -1 -1 -1 1 0 34.75
sub55 -1 -1 -1 0 1 36.54
sub56 -1 -1 -1 0 1 31.23
sub57 -1 -1 -1 -1 -1 23.98
sub58 -1 -1 -1 0 1 42.16
sub59 -1 -1 -1 1 0 42.99
sub60 -1 -1 -1 -1 -1 31.09
sub61 -1 -1 -1 -1 -1 38.5
sub62 -1 -1 -1 0 1 26.07
sub63 -1 -1 -1 0 1 38.96
sub64 -1 -1 -1 -1 -1 37.21
sub65 -1 -1 -1 -1 -1 41.09
sub66 -1 -1 -1 0 1 38.41
sub67 -1 -1 -1 -1 -1 35
sub68 -1 -1 -1 0 1 38.68
sub69 -1 -1 -1 -1 -1 25.98
sub70 -1 -1 -1 0 1 37.96
sub71 -1 -1 -1 -1 -1 37.5
sub72 -1 -1 -1 1 0 35.89
sub73 -1 -1 -1 1 0 45.88
sub74 -1 -1 -1 -1 -1 33.1
sub75 -1 -1 -1 1 0 31.84
sub76 -1 -1 -1 1 0 33.3
sub77 -1 -1 -1 0 1 46.65
sub78 -1 -1 -1 -1 -1 38.74
sub79 -1 -1 -1 1 0 39.78
sub80 -1 -1 -1 0 1 38.19
sub81 -1 -1 -1 0 1 44.06
sub82 -1 -1 -1 0 1 34.1
sub83 -1 -1 -1 0 1 34.05
sub84 -1 -1 -1 -1 -1 40.07
sub85 -1 -1 -1 0 1 38.31
sub86 -1 -1 -1 -1 -1 37.54
sub87 -1 -1 -1 0 1 41
