I perform prequential evaluation like this: start with a training set, classify a number of examples, then add the correctly classified examples in the training set and continue to classifying the next number of unseen examples. Is this supposed to increase performance as examples are added to the training set or this doesn't apply to every case? By increasing performance I mean if the average F1, not only accuracy, of the second piece of unseen examples must be higher than that of the first or is it possible for a latter piece to have worse average F1 than a former? And if it has worse, what does this could be possibly mean? Could it mean a problem with training data?
This paper Sentiment Knowledge Discovery in Twitter Streaming Data describes prequential evaluation. It experiments with Naive Bayes and not SVMs, probably for the reasons mentioned in comments below.
Thanks a lot in advance!