( ( Many women ) ( ( ( ( experience ( a decrease ) ) ( in ( progesterone levels ) ) ) ( as ( they age ) ) ) . ) )
(ROOT (S (NP (JJ Many) (NNS women)) (VP (VBP experience) (NP (DT a) (NN decrease)) (PP (IN in) (NP (JJ progesterone) (NNS levels))) (SBAR (IN as) (S (NP (PRP they)) (VP (VBP age))))) (. .)))
Many women experience a decrease in progesterone levels as they age.
(ROOT (S (NP (PRP You)) (ADVP (NP (NP (NN decrease) (NNS errors)) (PP (IN in) (NP (DT an) (NN experiment)))) (IN by)) (VP (VBP take) (NP (JJ many) (NNS measurements))) (. .)))