That's a very good question. I think the study of application to graduate departments at the University of California: Berkeley (often used in statistics textbooks as an example of Simpson's paradox) showed that what initially appeared as a bias in favor of male applicants was actually, when analyzed department by department, neutral admission or bias in favor of female applicants.
The self-selection involved in applying or not for a special program is surely relevant to analyzing bias, as you correctly point out. A different issue that other commenters here mention is whether participation in a school program at early elementary age has any necessary relation to adult career paths at later ages.
That's a very good question. I think the study of application to graduate departments at the University of California: Berkeley (often used in statistics textbooks as an example of Simpson's paradox) showed that what initially appeared as a bias in favor of male applicants was actually, when analyzed department by department, neutral admission or bias in favor of female applicants.
http://en.wikipedia.org/wiki/Simpson%27s_paradox#Berkeley_se...
The self-selection involved in applying or not for a special program is surely relevant to analyzing bias, as you correctly point out. A different issue that other commenters here mention is whether participation in a school program at early elementary age has any necessary relation to adult career paths at later ages.