Loranger questions whether the hypothesis that manic-depressive illness is transmitted through X-linked heredity can serve as a general explanation for all bipolar manic-depressive illness. His study shows the presence of father/son pairs to much the same degree as in other parent/child pairs. While the absence of these pairs in previous studies does not constitute the entire support for the hypothesis of X-linked transmission, the "probability values associated with these other findings are many magnitudes smaller than those found in studies of well established X-linked traits." Loranger concludes that the support for X-linkage "should be viewed as tentative and promising rather than definitive" and that while there is increasing evidence for X-linked transmission in "certain family pedigrees," whether they constitute a majority or a minority is yet to be determined.