It is also known as the law of large numbers. If the unreliability of the assessments are unreliable but the errors are independent, then the aggregates will be

It is also known as the law of large numbers. If the unreliability of the assessments are unreliable but the errors are independent, then the aggregates will be less unreliable. Of course this only holds if the unreliability is well behaved enough in the first place, which should hold here, since no single tweet can change the average sentiment of say 1000 tweets.