In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: RESULTS : After one year of electrical stimulation of the STN , the patients ' scores for activities of daily living and motor examination scores ( Unified Parkinson ' s Disease Rating Scale parts II and III ) off medication improved by 62 % and 61 % respectively ( p < 0 . 0005 ) .
### Output Text:
RESULTS : After one year of electrical stimulation of the STN , the patients ' scores for activities of daily living and motor examination scores ( Unified Parkinson ' s Disease Rating Scale parts II and III ) off medication improved by 62 % and 61 % respectively ( p < 0 . 0005 ) . 