  A common way to calculate the glitch activity of a pulsar is an ordinary
linear regression of the observed cumulative glitch history. This method
however is likely to underestimate the errors on the activity, as it implicitly
assumes a (long-term) linear dependence between glitch sizes and waiting times,
as well as equal variance, i.e., homoscedasticity, in the fit residuals, both
assumptions that are not well justified from pulsar data. In this paper, we
review the extrapolation of the glitch activity parameter and explore two
alternatives: the relaxation of the homoscedasticity hypothesis in the linear
fit and the use of the bootstrap technique. We find a larger uncertainty in the
activity with respect to that obtained by ordinary linear regression,
especially for those objects in which it can be significantly affected by a
single glitch. We discuss how this affects the theoretical upper bound on the
moment of inertia associated with the region of a neutron star containing the
superfluid reservoir of angular momentum released in a stationary sequence of
glitches. We find that this upper bound is less tight if one considers the
uncertainty on the activity estimated with the bootstrap method and allows for
models in which the superfluid reservoir is entirely in the crust.
