Proportional search interface usability measures

Speed, accuracy, and subjective satisfaction are the most common measures for evaluating the usability of search user interfaces. However, these measures do not facilitate comparisons optimally and they leave some important aspects of search user interfaces uncovered. We propose new, proportional measures to supplement the current ones. Search speed is a normalized measure for the speed of a search user interface expressed in answers per minute. Qualified search speed reveals the trade-off between speed and accuracy while immediate search accuracy addresses the need to measure success in typical web search behavior where only the first few results are interesting. The proposed measures are evaluated by applying them to raw data from two studies and comparing them to earlier measures. The evaluations indicate that they have desirable features.