48 Int. J. Operational Research, Vol. 15, No. 1, 2012 Copyright © 2012 Inderscience Enterprises Ltd. A unified scheme for developing software reliability growth models using stochastic differential equations P.K. Kapur* Department of Operational Research, University of Delhi, New Delhi, India E-mail: pkkapur1@gmail.com *Corresponding author Sameer Anand S.S. College of Business Studies, University of Delhi, New Delhi, India E-mail: sanand_or@yahoo.com Kalpana Yadav Indira Gandhi Institute of Technology, G.G.S.I.P. University, New Delhi, India E-mail: kyadav11@yahoo.com Jagvinder Singh Department of Operational Research, University of Delhi, New Delhi, India, E-mail: jagvinder.singh@gmail.com Abstract: Of late some continuous-state space software reliability growth model (SRGM) based on stochastic differential equations (SDEs) of Itô type (SDE-SRGM) has been proposed to assess software reliability. However, these SDE-SRGM does not differentiate between failure observation/detection and fault removal/correction processes. In this paper, we first develop a unified scheme for SDE-SRGM for the case when there is no differentiation between failure observation/detection and fault removal/correction processes, and then extend it for the case when there is a clear differentiation between failure observation/detection and fault removal/correction processes. The unified scheme presented in this paper is described by the failure observation/detection and fault removal/correction distributions. The unification scheme eases the task of model selection. The proposed models under the unification scheme have been validated using real data sets. Various comparison criteria results have been presented.