¥3dRegAna:
Qualitative Variables (ANCOVA)
HQualitative variables can also be used
åi.e., WeÕre modeling the response amplitude to a stimulus
of varying contrast when subjects are either young, middle-aged or old.
åX1 represents the stimulus contrast (quantitative): continuous
covariate
åCreate indicator variables X2 and X3 to represent age:
íX2 = 1 if subject is middle-aged
å = 0 otherwise
íX3 = 1 if subject is old (i.e.,
at least 1 year older than Bob Cox)
å = 0 otherwise
åFull Model (no interactions between age and contrast)
íY = b0 + b1X1 + b2X2 +
b3X3 +
e
E(Y) = b0 + b1X1 for young
subjects
E(Y) = ( b0 + b2 ) + b1X1 for middle-aged
subjects
E(Y) = ( b0 + b3 ) + b1X1 for old subjects
åFull Model (with interactions between age and contrast)
íY = b0 + b1X1 + b2X2 +
b3X3 +
b4X2X1 +
b5X3X1 +
e
E(Y) = b0 + b1X1 for young
subjects
E(Y) = ( b0 + b2 ) + ( b1 + b4 )X1 for
middle-aged subjects
E(Y) = ( b0 + b3 ) + ( b1 + b5 )X1 for old subjects
HWill be easier to run analysis in Matlab script for 3dANOVA4, when
ready!