1995A&A...304..341B

We propose a method for estimation of the time delay between identical time samples with unequidistant data. We carried out an analysis of two published optical data sets (Vanderriest et al. 1989A&A...215....1V; Schild 1990AJ....100.1771S) of Q 0957+561 A, B, the first gravitational lens. It is determined that the time delay between the arrival of wave fronts from the images A and B is 1.45+0.04yr. Using Monte-Carlo simulations, we compare reliability of time delay determination methods and define the confidence probability of our result better than 99%. The problem of microlensing effects is briefly discussed.