No statistically significant associations were found between ABO blood group distributions and RDC subtype diagnoses in 79 subjects with unipolar (single episode and recurrent) and bipolar major depressive disorder using data from our sample. We discuss methodological issues related to the control samples and choice of statistical methods in the reported studies which have looked for associations between ABO blood types and patients diagnosed as having an affective disorder. After presenting our rationale for employing the logarithm of the cross product ratio (lambda) in place of the more traditionally utilized chi-squared, we used lambda to reanalyze the original data from nine studies in the literature. The individual studies are equivocal on the basic issue of an association between type O blood and bipolar I illness, either compared to controls or to recurrent unipolar patients. The combined (weighted average) measure of association indicates a small but definite association, but statistical analysis of the dispersion of the individual estimates around this combined estimate reveals that the studies have a higher degree of heterogeneity in results than expected by chance. The consequences of this finding are discussed, and possible explanations are offered.
ABO Blood-Group System Bipolar Disorder