Sliding-window multi-stream join (SWMJ) is a fundamental operation for correlating information from different streams. We provide a solution to the problem of assessing significance of the SWMJ result by focusing on the relative frequency of windows satisfying a given equijoin predicate as the most important parameter of the SWMJ result. In particular, we derive a formula for computing the expected relative frequency of windows satisfying a given equijoin predicate that can be evaluated in quadratic time in the window size given a proposed probabilistic model of the multi-stream. In experiments conducted on a daily rainfall data set we demonstrate the remarkable accuracy of our method, which confirms our theoretical analysis. © 2012 Higher Education Press and Springer-Verlag Berlin Heidelberg.