(S (S (BASENP (DT The) (NN research)) (VP (VBD followed) (NP (BASENP (RB about) (NN half)) (PP (IN of) (NP (NP (BASENP (DT a) (NN pool)) (PP (IN of) (BASENP (NN 439) (NNS adolescents)))) (SBAR (WHNP (WP who)) (S (VP (VBD had) (VP (VP (VBN received) (NP (BASENP (NN treatment)) (PP (IN for) (BASENP (JJ major) (NN depression))))) (CC and) (VP (VBN volunteered) (PP (IN for) (BASENP (NNP Duke) (NNP University) (NN research))))))))))))) (PERIOD .))