A good catch by commenter Raj:
Candidates appearing for JEE prepare either through “self study” or through “specialized teaching (other)”. Data (Table A8) for JEE 2011 shows that 295618 out of 468280 (63.1%) have prepared using “self study”. Out of the 13196 candidates who qualified, 4912 (37.22%) have used the “self study” mode.
What are the odds that the sociological data collected by JEE is just deceptive fluff? [And, yes, this probably means the income effect is tainted as well].