Interpretation for Worst and Average Case Analysis Alessandra Di Pierro1 , Chris Hankin2 , and Herbert Wiklicky2 1 Dipartimento di Informatica, University of Pisa, Italy 2 Department of Computing, Imperial College London, UK Abstract. We review Wilhelm's work on WCET for hard real-time applications and also recent work on analysis of soft-real time systems using probabilistic methods. We then present Probabilistic Abstract Interpretation (PAI) as a quantitative variation of the classical approach; PAI aims to provide close approximations