(S (S (NP (BASENP (DT A) (JJ representative) (JJ nationwide) (NN sample)) (PP (IN of) (NP (BASENP (NN 820) (NNS teens)) (ADJP (BASENP (QP (NN 14) (SYM --) (NN 17)) (NNS years)) (JJ old))))) (VP (VP (VBD participated) (PP (IN in) (BASENP (DT the) (NN study)))) (PP (IN with) (BASENP (JJ parental) (NN permission))))) (PERIOD .))