When is a proportional hazards model valid for both stock and flow sampledduration data?

It is shown that if the flow-sampled total durations and stock-sampled elap sed durations from stationary renewal processes both exhibit proportional h azard rates and are continuous then they belong to the family of survival d istributions with linear mean residual functions introduced by Hall and Wel lner (1984) [Hall, W.J., Wellner, J.A., 1984. Mean residual life. In: Csorg o, M., Dawson, D.A., Rao, J.N.K., Saleh, A.K.M.E., (Eds.), Proceedings of t he International Symposium on Statistics and Related Topics. North Holland, Amsterdam, pp. 169-184]. (C) 2000 Elsevier Science S.A. All rights reserve d.