I average around .228
There are a couple of factors that could translate into a lower score or faster score. The speed of your computer, if the clock runs faster or slower then it should. The bus speed of device you're using, you mouse is plugged into USB or PS2. The speed of your mouse, does your mouse process clicks faster or slower. Of course these would only be 100ths to 1000ths of a second differences.
So while this test is not 100% accurate, it does give you a good guess on what your reaction speed is. Of course, it's just measuring how fast you can process the signal and tell your body to do something and how well you can focus. Clicking a button is one of the easiest things you can do.
Also, while I was staring at the dot, my mind kept telling me it was going to be yellow and I started to see the dot change to yellow before it did. I tried to preceive the change before it happened and I was slower at distinguishing the change. The other thing I noticed was when I wasn't staring at the dot and just looking at the screen, my time would be faster.
Also, Casey found this on improving reaction speed.
http://www.aboutmartialarts.info/articl ... sh_etc.php