How often are scientific theories overturned?

The Dilbert cartoonist posts whimsical ideas all the time, but only gets hate mail if he says something skeptical about biological evolution or global warming. Those are sacred cows of today's intellectual left.

He now writes:

Let's get this out of the way first...

In the realm of science, a theory is an idea that is so strongly supported by data and prediction that it might as well be called a fact. But in common conversation among non-scientists, "theory" means almost the opposite. To the non-scientist, calling something a theory means you don't have enough data to confirm it.

I'll be talking about the scientific definition of a theory in this post. And I have one question that I have seen asked many times (unsuccessfully) on the Internet: How often are scientific theories overturned in favor of new and better theories? ...

Note to the Bearded Taint's Worshippers: Evolution is a scientific fact. Climate change is a scientific fact. When you quote me out of context - and you will - this is the paragraph you want to leave out to justify your confused outrage.

He has taken his definition of theory from his evolutionist critics, like PZ Myers, but I do not see the term used that way. Physicists use terms like "string theory" even tho it is not supported by any facts or data at all.

I also don't see non-scientists using the word to mean the opposite. Not often, anyway. The first I saw was when Sean M. Carroll was on PBS TV explaining BICEP2 and cosmic inflation. As you can see in the video, the dopey PBS news host asks:

Those predictions have always been theories. How do you then go about proving a theory not to be a theory, and is that what we have actually done here? Has it been proven? [at 2:50]

With exceptions like this, my experience is that scientists and non-scientists use the term "theory" in the same say. Eg, global warming is a theory whether you accept the IPCC report or not.

A comment points out the Wikipedia article: Superseded scientific theories.

To answer the question, you first have to agree on what an overturned theory is. Did Copernicus overturn Ptolemy? Did general relativity overturn Newtonian gravity?

I would say that these theories were embellished, but not overturned. The old theories continued to work just as well for nearly all situations.

You might say that the Bohr atom has been overturned, but it was never more than a heuristic model, and it is still a good heuristic model. Not as good as quantum mechanics, but still a useful way of thinking about atoms.