It's not ideal, but you an learn a lot from watching people use a web site. Keith Instone 's Usable Web site has a couple dozen links to user testing information that will get you started. Another form of observational primary research is gleaned from the logging built into online activity and from the measurability inherent to technical information. At its most basic level the Internet is just a string of ones and zeros and computers are terrific counting machines. Learn more about these metrics .
Experiments establish cause and effect relationships.
However, controlling for variables such as the 4 P's is difficult in real-world situations. We're reluctant to experiment on people. Not everything that can be counted counts, and not everything that counts can be counted. They help people describe reasons for their behavior, but surveys can be plagued by problems in completion. They presume self-knowledge and a willingness to reveal it.