Thresholds for object-oriented measures

A practical application of object oriented measures is to predict which classes are likely to contain a fault. This is contended to be meaningful because object oriented measures are believed to be indicators of psychological complexity, and classes that are more complex are likely to be faulty. Recently, a cognitive theory was proposed suggesting that there are threshold effects for many object oriented measures. This means that object oriented classes are easy to understand as long as their complexity is below a threshold. Above that threshold their understandability decreases rapidly, leading to an increased probability of a fault. This occurs, according to the theory, due to an overflow of short-term human memory. If this theory is confirmed, then it would provide a mechanism that would explain the introduction of faults into object oriented systems, and would also provide some practical guidance on how to design object oriented programs. The authors empirically test this theory on two C++ telecommunications systems. They test for threshold effects in a subset of the Chidamber and Kemerer (CK) suite of measures (S. Chidamber and C. Kemerer, 1994). The dependent variable was the incidence of faults that lead to field failures. The results indicate that there are no threshold effects for any of the measures studied. This means that there is no value for the studied CK measures where the fault-proneness changes from being steady to rapidly increasing. The results are consistent across the two systems. Therefore, we can provide no support to the posited cognitive theory