Tests of randomness Statistical analysis has in practice been much more concerned with finding regularities in data than in testing for randomness. … (These difficulties provided yet more support for my contention that models with intrinsic randomness are more reliable than those with external randomness.) … And occasionally people have told me that their tests have found deviations from randomness.

Time series Sequences of continuous numerical data are often known as time series, and starting in the 1960s standard models for them have consisted of linear recurrence relations or linear differential equations with random noise continually being added. … As discussed on page 919 it was already realized in the 1970s that even without external random noise nonlinear models could produce time series with seemingly random features.