While the neutron lifetime has been studied for decades, there currently exists a lack of consilience on its exact value, due to different results from two experimental methods ("bottle" versus "beam"). The "neutron lifetime anomaly" was discovered after the refinement of experiments with ultracold neutrons. While the error margin was once overlapping, increasing refinement in technique which should have resolved the issue has failed to demonstrate convergence to a single value. The difference in mean lifetime values obtained as of 2014 was approximately 9 seconds. Further, a prediction of the value based on quantum chromodynamics as of 2018 is still not sufficiently precise to support one over the other. As explained by Wolchover (2018), the beam test would be incorrect if there is a decay mode that does not produce a proton.