The frequency of misattributed paternity in Sweden is low and decreasing: A nationwide cohort study

Background: The occurrence of misattributed paternity has consequences throughout society with implications ranging from inheritance and royal succession to transplantation. However, its frequency in Sweden is unknown. Objective: To estimate the contemporary frequency of misattributed paternity in Sweden. Methods: The study was based on nationwide ABO blood group data and a nationwide register of familial relationships in Sweden. These data were analysed using both a frequentist Poisson model and the Bayesian Gibbs model. The conduct of the study was approved by the regional ethics committee in Stockholm, Sweden (reference numbers 2018/167-31 and 2019-04656). Results: Nearly two million mother-father-offspring family units were included. Overall, the frequency of misattributed paternity was estimated at 1.7% in both models. Misattributed paternity was more common among parents with low educational levels, and has decreased over time to a current 1%. Conclusions: The misattributed paternity rate is similar to the rates in other West-European populations. Apart from widespread societal implications, studies on heritability may consider misattributed paternity as a minor source of error.