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: The mean + / - SD number of days of delirium during hospitalization was lower in the light sedation group than in the deep sedation group ( 0 . 5 + / - 1 . 5 days vs 1 . 4 + / - 4 . 0 days ; P = . 01 ) .
### Output Text:
The mean + / - SD number of days of delirium during hospitalization was lower in the light sedation group than in the deep sedation group ( 0 . 5 + / - 1 . 5 days vs 1 . 4 + / - 4 . 0 days ; P = . 01 ) . 