I got stuck trying to find a good definition of “socioeconomic status” recently. Maybe there isn’t one. Here is a bunch of reading on the matter:
http://en.wikipedia.org/wiki/Socioeconomic_status
http://www.apa.org/pi/ses/resources/publications/factsheet-education.aspx
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2465546
http://www.ncbi.nlm.nih.gov/pubmed/3241948
http://www.annualreviews.org/doi/full/10.1146/annurev.publhealth.18.1.341
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2792081/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1447206
http://psycnet.apa.org/journals/amp/49/1/15/
http://www.ajpmonline.org/article/S0749-3797(07)00314-5/fulltext
http://www.ncbi.nlm.nih.gov/pubmed/19178922
http://www.jstor.org/stable/27522200
http://heapol.oxfordjournals.org/content/21/6/459.long