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: Based on Bayes ' theorem and the first model , the predictive accuracy of identifying patients not cured increased from 0 . 19 to 0 . 83 .
### Output Text:
Based on Bayes ' theorem and the first model , the predictive accuracy of identifying patients not cured increased from 0 . 19 to 0 . 83 . 