The strengths and limitations of the study
The main strength of the present study is that, for the first time, the subjects were genotyped by a molecular method. In previous studies, either the genotypes were estimated based on the phenotype of parents, or only the effects of Rh phenotypes, not Rh genotypes, were studied. Another important advantage is that the Rh phenotypes/genotypes were estimated in the course of a study and not self-reported by the participants of the study.
The main limitation of the study is that subjects reported their health problems themselves. It is clear that some people might misreport their health problems. However, there is no reason to expect that Rh-positive heterozygotes and homozygotes (mis)reported their problems differently unless they really differ in their health status. It is important to remember that participants were not aware of their RhD genotype at the time of filling the questionnaire. Another limitation of the present study is that participants have been self-selected and therefore probably do not represent a typical Czech population. The observed higher prevalence of Rh-negative subjects among the participants (24.2 % in women and 27.2 % in men) than in the general Czech population (16 %) (a phenomenon reported also in all previous Czech studies on volunteers, reviewed in (Flegr, Toman, et al., 2020)) suggests that Rh-negative subjects have a higher willingness to participate in unpaid scientific studies.