**8. Publication bias**

Publication bias is a problem with any review because "studies with results that are significant, interesting, from large well-funded studies, or of higher quality are more likely to be submitted, published, or published more rapidly than work without such characteristics" (Sutton, 2000). Therefore, it is possible that other relevant dietary intervention studies with genotype information exist but were not included in this review because they have not been published. It is possible that the literature strategy for this review missed studies because the genotype analyses were not mentioned in their title, abstract, or subject headings (Masson et al, 2003).

In the search for explanations for the heterogeneity in lipid responses, reviewers may tend to highlight studies showing significant effects of genetic variation while ignoring a large proportion of studies that found no such results. Studies showing nonsignificant or conflicting results cannot be ignored, especially because they outnumber the studies showing significant effects, notwithstanding the unpublished studies that could have nonsignificant and uninteresting results. Therefore, one has to ask the question "If genetic variability plays a role in the heterogeneity of lipid and lipoprotein responses to dietary change, why have so many studies been unable to demonstrate this with statistical significance?" (Masson et al, 2003).
