Thanks for the advice Malignon. I just asked my dad for evidence from his doctor, I hope it helps. How long does it take to hear back from USCIS to know if I have been approved or not?
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Application sent: 8/24/2012
USCIS received my application: 8/30/2012
I received my appointment letter: 9/15/2012 (appointment for 10/04, 8am)
Biometrics taken: 10/04/2012 at 8am
Approved via online: 10/22/2012