Check A Checkbox Depending On Page Content

I'm trying to write a piece of javascript that will check a single checkbox depending on a dynamically-imported piece of information further up the page. The page will look like this:

[Code]....

The variable which indicates which checkbox should already be checked is in the div 'title' in the p class 'white'. So in the case above, when the page loads the 'Option 1' checkbox should already be checked. The javascript i have, rather poorly, cobbled together so far just doesn't work, and I was wondering if anyone could point me in the direction of some useful tutorials. All the tutorials I have read so far deal with mass checking all the boxes with a button click.