• The amount of **data** N required to detect a breakdown of linear response for a given perturbation size can be very large. For the logistic map with a given perturbation size of the order of ε = O(10 −6 ) one needs at least N = 600, 000 for a smooth observable A(x) = x. Hence, an apparent linear response seen in a given time series might be spuriously caused by an insufficient quantity of data.