This document presents research into the relationship between class evolution patterns and fault proneness in object-oriented programs. The researchers analyzed three open-source programs to classify classes based on their lifetimes and coevolution with other classes. They found that persistent classes that exist throughout the program's lifetime were significantly less fault-prone than short-lived or transient classes. Additionally, faults involving coevolved classes that changed together over time accounted for a significantly higher proportion of fixed faults than non-coevolved classes. The results provide empirical evidence that class evolution patterns correlate with fault proneness and have implications for fault detection and prevention strategies.