Precise modern instrumentation that requires an essentially alveolar sample will ensure breath test precision. The collection of two breath samples from each individual provides confidence in results and allows for the evaluation of data by means of a t-test for paired data. Bearing in mind that the power of the t-test increases with sample size, but considering the clinical or forensic differences, reveals no meaningful difference between two intra-individual breath samples collected approximately 3 minutes apart. (Publisher abstract)