Psychology
He uses statistics as a drunken man uses lampposts — for support rather than illumination.Andrew Lang
Peter Norvig wrote an excellent article on how to conduct empirical studies and how to interpret the resulting data.
When you have to deal with cognitive psychology it is absolutely necessary to know how our brain works and which different brain areas interact with each other. Luckily I've recently found a nice tutorial video on youtube about this.
Have fun.
About 8-9% of all men and 1% of all women are “color-blind” (reference). If you ignore this while designing an application or website you're ignoring nearly 4 million people in germany alone.
But how can one check whether the application/site is useable by everyone?
