Reproducibility and repeatability.

pressure and inter-beat interval variability in man. Apart from that the topic of the study is interesting and important, the paper contains some terminological inconsistencies which seriously undermine implications of research and thus, credibility of the conclusions made by the Authors. It is not uncommon to find studies with inconsistent terminology and definitions, with some terms being defined differently but then used interchangeably. Inconsistency in the use of terminology makes it difficult to determine what methodology, both, experimental and analytical, is being used in the research. The terms " reproducibility " and " repeatability " are both strictly defined, each with its own, unique meaning, and scientists should distinguish between them. Reproducibility of a method/test can be defined as the closeness of the agreement between independent results obtained with the same method on the identical subject(s) (or object, or test material) but under different conditions (different observers, laboratories etc.). In a specific situation, it can be defined as the variability of the measurement system caused by differences in the observer's behavior. In mathematical terms, it is the variability of the average values obtained by several observers while measuring the same item (interobserver variability). On the other hand, repeatability denotes the closeness of the agreement between independent results obtained with the same method on the identical subject(s) (or object or test material), under the same conditions. Or, it is the variability of the measurements obtained by one person while measuring the same item repeatedly (intraobserver variability). This is also known as the inherent precision of a measurement equipment (BS ISO 5725 part 1 and part 2, IUPAC 1997, Engineered Software 1999). Among the statistical methods for determination of repeatability and reproducibility, the most frequently used procedure is that proposed by Bland and Altman (1986). From the presented paper, it is not clear whether the Authors have been distinguishing between the discussed terms and whether they used appropriate statistical methods to answer the aim of the study addressed in the title. From the data acquisition and analysis described in the Methods section, it can be inferred that they rather assessed repeatability of the measurements than determined reproducibility. As mentioned above, the term reproducibility is associated with the method, observer, laboratory etc., and not with the measured variable itself as it is indicated in the title. This apparent misunderstanding and confusion of the terms " repeatability " and " reproducibility " has raised …