... observe how the fraction of query traffic con-taining the phrase1changes over time. For instance,as shown next, the fraction of query traffic contain-ing “how to” has in fact been going up since ... that the decreasing gap in search quality (as measuredby click positions) might have contributed to the in- crease in Q -level, if we examine the co-click datawithout the stability constraint, ... thiscoincides with the rise in popularity of community-based Q&Asites.Q-rate than the light users. And for the most heavyusers, the Q-rate tapers down.Furthermore, taking the data from the...