Crowdsourcing is a popular technique to collect large amounts of human-generated labels, such as relevance judgments used to create information retrieval (IR) evaluation collections. Previous research has shown how collecting high quality labels from a crowdsourcing platform can be challenging. Existing quality assurance techniques focus on answer aggregation or on the use of gold questions where ground-truth data allows to check for the quality of the responses. In this paper, we present qualitative and quantitative results, revealing how different crowd workers adopt different work strategies to complete relevance judgment tasks efficiently and their consequent impact on quality. We delve into the techniques and tools that highly experienced crowd workers use to be more efficient in completing crowdsourcing micro-tasks. To this end, we use both qualitative results from worker interviews and surveys, as well as the results of a data-driven study of behavioral log data (i.e., clicks, keystrokes and keyboard shortcuts) collected from crowd workers performing relevance judgment tasks. Our results highlight the presence of frequently used shortcut patterns that can speed-up task completion, thus increasing the hourly wage of efficient workers. We observe how crowd work experiences result in different types of working strategies, productivity levels, quality and diversity of the crowdsourced judgments.
