Introduction: Bias and precision statistics have succeeded regression analysis when measurement techniques are compared. However, when applied to cardiac output measurements, inconsistencies occur in reporting the results of this form of analysis.
Methods: A MEDLINE search was performed, dating from 1986. Studies comparing techniques of cardiac output measurement using bias and precision statistics were surveyed. An error-gram was constructed from the percentage errors in the test and reference methods and was used to determine acceptable limits of agreement between methods.
Results: Twenty-five articles were found. Presentation of statistical data varied greatly. Four different statistical parameters were used to describe the agreement between measurements. The overall limits of agreement in studies evaluating bioimpedance (n = 23) was +/-37% (15-82%) and in those evaluating Doppler ultrasound (n = 11) +/-65% (25-225%). Objective criteria used to assess outcome were given in only 44% of the articles. These were (i) limits of agreement approaching +/-15-20%, (ii) limits of agreement of less than 1 L/min, and (iii) more than 75% of bias measurements within +/-20% of the mean. Graphically, we showed that limits of agreement of up to +/-30% were acceptable.
Conclusions: When using bias and precision statistics, cardiac output, bias, limits of agreement, and percentage error should be presented. Using current reference methods, acceptance of a new technique should rely on limits of agreement of up to +/-30%.