Lumpers look for universal rules and valid generalizations about human behavior.
Splitters are more interested in studying how individuals differ from each other. Many of the discussions in this hypertext book The Psychology of Cyberspace comes from the splitter's perspective. Much of it is based on psychological theory and conceptualization. It's been a few years since I first posted these stats, so they are dated now. Nevertheless, even this old data raises important questions about how demographic factors might influence the social dynamics of cyberspace, as well as how cyberspace reflects the global culture.