  Effective operators have been used extensively to understand small deviations
from the Standard Model in the search for new physics. So far there has been no
general method to fit for small parameters when higher order corrections in
these parameters are present but unknown. We present a new technique that
solves this problem, allowing for an exact p-value calculation under the
assumption that higher order theoretical contributions can be treated as
gaussian distributed random variables. The method we propose is general, and
may be used in the analysis of any perturbative theoretical prediction,
ie.~truncated power series. We illustrate this new method by performing a fit
of the Standard Model Effective Field Theory parameters, which include
eg.~anomalous gauge and four-fermion couplings.
