( ( In ( this experiment ) ) ( ( ( the ( independent variable ) ) ( -LRB- ( factor -RRB- ) ) ) ( ( is ( ( the amount ) ( of ( ( practice , ) ( called ( factor A ) ) ) ) ) ) . ) ) )
(ROOT (S (PP (IN In) (NP (DT this) (NN experiment))) (NP (NP (DT the) (JJ independent) (NN variable)) (PRN (-LRB- -LRB-) (NP (NN factor)) (-RRB- -RRB-))) (VP (VBZ is) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN practice)) (, ,) (VP (VBN called) (NP (NN factor) (NN A))))))) (. .)))
In this experiment the independent variable (factor) is the amount of practice, called factor A .
(ROOT (S (NP (NP (DT The) (NNS values)) (PP (IN of) (NP (JJ independent) (NNS variables)))) (VP (VBP are) (VP (VBN controlled) (PP (IN by) (NP (NP (DT the) (NN experimenter)) (PP (IN over) (NP (NP (DT the) (NN course)) (PP (IN of) (NP (DT an) (NN experiment))))))))) (. .)))