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: Fewer than 6 % of patients in either group were considered by the investigator to have a worsening of their overall disease condition during the study .
### Output Text:
Fewer than 6 % of patients in either group were considered by the investigator to have a worsening of their overall disease condition during the study . 