what types of data comes in chat activity - Agent

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can anyone explain what kind of data comes in chat activity - Agent standard report which is located under \Public Reports\Service\Chat Reports location, i am asking this because i ran couple of standard report like Response Time which tells number of chats that were accepted by System during each interval, Chat Agent - Activity : description says count the actual number of chats which agent completed during their session, i ran Response Time report for 3rd of august where i got 211 chats (these are the total chats which accepted by agents)  and but when i run Chat Agent - Activity report for same day i get 200 chats only.