Posing a question to an online question and answer community does not guarantee a response. Significant prior work has explored and identified members" motivations for contributing to communities of collective action (e.g., Yahoo! Answers); in contrast it is not well understood why members choose to not answer a question they have already read. To explore this issue, we surveyed 135 active members of Yahoo! Answers. We show that top and regular contributors experience the same reasons to not

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... wer a question: subject nature and composition of the question; perception of how the questioner will receive, interpret and react to their response; and a belief that their response will lose its meaning and get lost in the crowd if too many responses have already been given. Informed by our results, we discuss opportunities to improve the efficacy of the question and answer process, and to encourage greater contributions through improved design.