1. A method for determining a class for at least one data item, the method comprising: inputting a data item into a scoring classifier such that the scoring classifier indicates that the data item belongs to a first class; determining an amount of retraining of the scoring classifier that is required to cause the scoring classifier to indicate that the data item belongs to a second class that is different from the first class; determining a reliability measure based on the required amount of retraining; and determining a class of the data item based, at least in part, on the reliability measure.