We investigate the problem of evaluating the reliability of a magnetostratigraphic section using a jackknife resampling scheme. We define a parameter, J as the slope relating the percentage of polarity zones of a sampled section remaining after random deletion of sites increasing in proportion to a total of 20% of the initial collection. So defined, J quantifies the dependence of a magnetostratigraphic record on the distribution of sampling sites. Based on simulated magnetostratigraphic sections, J was found to be an indicator of the approximate percentage of polarity zones present in the original reference sections that were recovered in the sampled section. J will perhaps be most helpful as a guide to investigators as to whether further sampling would provide useful information as well as to the non‐paleomagnetist user of black and white interpretive polarity logs as an estimate of the reliability of a given section.