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: Similar decreases were observed in both groups , with no statistically significant differences between the groups for any variable analyzed .
### Output Text:
Similar decreases were observed in both groups , with no statistically significant differences between the groups for any variable analyzed . 