However, such results as were statistically significant did not fall into a readily discernible pattern. A particular difficulty is that the experiments were not well designed. For example, there is very little information about how the GM and control diets differed in their detailed composition, and in particular about differences other than those attributable to the inserted gene. These differences should have been fully analysed, and addressed by using several distinct strains of GM potato in the feeding trials. Third, when a rat is underfed many organs are likely to be affected, so that separate measurements on the same specimen will turn out to be interrelated.
Unconscious bias is well known to be a source of invalid results.
Because of the poor experimental design, it is simply not possible to be sure about the causes of the small effects obtained in the study. It had been claimed that the consumption of GM potatoes had significant effects on the immune system of rats in the feeding trials, because of some effect of the genetic modification itself rather than because of the particular gene inserted. Reviewers were asked to consider if this conclusion was valid. One of the immune reactions in the body can be mimicked in the laboratory. This provides a means of testing for effects on the immune system.