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A new critical survey is presented of all half-life, decay-energy andbranching-ratio measurements related to 20 superallowed 0+ --> 0+ beta decays.Included are 222 individual measurements of comparable precision obtained from177 published references. Compared with our last review in 2008, we have addedresults from 24 new publications and eliminated 9 references, the results fromwhich having been superseded by much more precise modern data. We obtainworld-average ft-values for each of the eighteen transitions that have acomplete set of data, then apply radiative and isospin-symmetry-breakingcorrections to extract corrected Ft values. Fourteen of these Ft values nowhave a precision of order 0.1% or better. In the process of obtaining theseresults we carefully evaluate the available calculations of theisospin-symmetry-breaking corrections by testing the extent to which they leadto Ft values consistent with conservation of the vector current (CVC). Only oneset of calculations satisfactorily meets this condition. The resultant averageFt value, when combined with the muon liftime, yields the up-down quark-mixingelement of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, Vud = 0.97417 +/-0.00021. The unitarity test on the top row of the matrix becomes |Vud|^2 +|Vus|^2 + |Vub|^2 = 0.99978 +/- 0.00055 if the Particle Data Group recommendedvalue for Vus is used. However, recent lattice QCD calculations, not includedyet in the PDG evaluation, have introduced some inconsistency into kaon-decaymeasurements of Vus and Vus/Vud. We examine the impact of these new results onthe unitarity test and conclude that there is no evidence of any statisticallysignificant violation of unitarity. Finally, from the Ft-value data we also setlimits on the possible existence of scalar interactions.

Superallowed 0+ --> 0+ nuclear beta decays: 2014 critical survey, with precise results for Vud and CKM unitarity