**math.ST Statistics**

- Accurate polling; testing of medical treatments; fraud detection (e.g. via Benford's law)

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Well, this was quick :-)

I don't have enough points to edit the wiki articles, so I guess I'll just toss a few here to get merged into the wiki articles:

math.CA:  Fourier analysis allows one to precisely divide up the electromagnetic spectrum, leading of course to radio, television, wireless, and so forth.  MRI is based on inverting the Radon transform.