Is reputation on Stack Overflow always a good indicator for users' expertise? No!

Stack Overflow (SO) users are recognized by reputation points. The reputation points are often a great avenue for users to build their career profile and demonstrate their expertise in some domains. Prior studies used users' reputation as a proxy to estimate their experience and expertise. However, there are various ways for a user to earn reputation points that do not require much expertise, such as asking high-quality questions. Therefore, it is important to understand the meaning of a high-reputation point and if the reputation could be used as a good indicator for users' expertise and experience on Stack Overflow. In this study, we explore how users earn reputation points on Stack Overflow by mining their reputation-related activities (e.g., asking questions, answering questions, and editing posts). We study the reputation-related activities of 93,053 high-reputation users that have at least 1,000 reputation points. We find that 1) 13.8% of the studied users earn their majority reputation points through asking questions rather than answering questions. 2) In general, most of the posted answers received no or very few reputation points with users gaining their points from a very small proportion of highly-voted answers. 12% of users' entire reputation comes from one single answer. We suggest future research and Stack Overflow introduce a new metric (i.e., vindex) to evaluate the expertise of a user.