Did SF Plastic Bag Ban Increase Dog Doo Messes?

The other day I was telling a co-worker about this blog.  We compared notes about why there's been an increase in dog droppings left behind. He theorized that perhaps it was caused by the San Francisco ban that stops grocery stores from using plastic bags.

What do you think? Is there any evidence that suggests this might be true?

Poo Fighters Unite! - Wear this proudly:
No Dog Doo Allowed - 3.5" Button