Another caveat to consider is sampling error. Since the studied precancerous conditions tend to be patchy lesions, there is always a risk for false negative results.25 It was not possible to obtain detailed information about the subsite being biopsied, and when gastroscopy was repeated, whether the biopsy samples were taken from the same mucosal area. Inability to capture the stomach’s most advanced lesion leads to some overestimation of the incidence of gastric cancer in groups classified as having less advanced lesions, and an underestimation of the range from the lowest to the highest incidence. As already noted, however, the incidence in the normal group was not very different from that expected in the matched population, and a change downward in Correa’s cascade proved to be followed by a lower incidence of gastric cancer. These reassuring observations suggest that our results were not unduly affected by sampling error, and also that true reversion of Correa’s cascade might be possible. The latter conclusion is at odds with the literature.31 32 33 In addition, since all biopsy samples were taken in routine healthcare and were assessed by many different pathologists, inter-observer and intra-observer variation was a reality, despite the fact that the practice guidelines for the standardised disease diagnosis were set up by the Swedish Society for Pathology. Also, given the prospective design and the two year latency, which essentially removed all prevalent cases of gastric cancer, the misclassification was non-differential for the gastric cancer outcome. The resulting error may have led to conservative estimates of the differences in gastric cancer rate between mucosal histology groups.