What does Raven's SPM even measure? Would you expect any difference in SPM scores between groups with good socio-economic status v/s poor socio-economic status or with exposure to good schools? #psychology #statistics

Need some help with this graph. SPM should be culture-fair & not depend on participants' SES But it seems like people with higher SPM scores come from good SES bg with more English & less Hindi exposure & people with low SPM scores from homes where exposure of Hindi is good against my intuitions.