Applied Marketing Science (AMS) participated in a study to help determine “network effects” in a major antitrust suit against a computer software manufacturer. Together with our expert, we conducted a conjoint study of the projected penetration of a hypothetical new brand of desktop software. We designed a computer-based study of consumer and business purchasers, which asked respondents to consider a hypothetical new operating system-productivity suite combination. The characteristics considered in the study included price, the percentage of computer users who had adopted the new software, and the availability of customer support. We found that when the respondents were asked to consider equally functional operating system-productivity suite combinations, the one that had a higher installed base was the preferred brand, thereby supporting the manufacturer’s position.