The International Collaborative Study (ICS) involved a wide range of sample materials and ages and, on completion, assessed each stage independently (Scott et al. 1989; Aitchison et al. 1990). Here, the three stages of the study are combined and an overview is provided of the uncertainties in the dating procedure as a whole and in its component processes. Reports three key optimal performance indices, related to internal and external precision and to bias, which have been defined to allow quantitative assessment of Internal Consistency and External Consistency (Aitchison et al. 1990). These measures provide quantitative descriptions of a laboratory's reproducibility, accuracy, and precision in the authors' opinion. For the internal consistency, the Internal Error Multiplier of the quoted error is defined and, for the external consistencty of any laboratory relative to an appropriate baseline, two indices have been defined, the Systematic Bias and External Error Multiplier of the quoted error. The three indices over the three stages have been evaluated and the relative performances of gas counting, accelerator and liquid scintillation laboratories have been assessed. The quoted errors describe adequately the variability in duplicate results, but there is evidence of systematic biases and underestimation of interlaboratory variability. The contribution of pretreatment, synthesis, and counting to the overall variability for each laboratory type have been considered. Reports that, for liquid scintillation (LS) and gas counting (GC) laboratories, ca. 66% of the total variation is due to counting and sample synthesis whereas, for accelerator mass spectrometry (AMS) laboratories, the major sources of variability are the sampling and pretreatment processes.