(1) Compensation For purposes of this section, the term “compensation” includes earned income (as defined in section 401(c)(2) ). The term “compensation” does not include any amount received as a pension or annuity and does not include any amount received as deferred compensation. For purposes of this paragraph, section 401(c)(2) shall be applied as if the term trade or business for purposes of section 1402 included service described in subsection (c)(6). The term “compensation” includes any differential wage payment (as defined in section 3401(h)(2)). The term “compensation” shall include any amount which is included in the individual’s gross income and paid to the individual to aid the individual in the pursuit of graduate or postdoctoral study.