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Herd, Clare P., Claire L. Tomlinson, Katherine HO Deane, Marian C. Brady, Christina H. Smith, Catherine M. Sackley, a Carl E. Clarke. "Speech and Language Therapy Versus Placebo or No Intervention for Speech Problems in Parkinson's Disease." Cochrane Database Syst Rev 2012.

Herd, Clare P., et al. "Speech and Language Therapy Versus Placebo or No Intervention for Speech Problems in Parkinson's Disease." Cochrane Database Syst Rev 2012.