Task: Question Answering
Input (English): . A highly dynamic community constantly shifts interests from one time window to another, and these temporal variations are reflected in its use of volatile language. Formally, we define the dynamicity of a community INLINEFORM0 as the average volatility of all utterances in INLINEFORM1 .  
 Question: How do the authors measure how temporally dynamic a community is?
Output (English): the average volatility of all utterances