When repeated measurements (replicates) are made for each subject, it is inefficient
to estimate average bias and limits of agreement using only the first measurement, rather
than all measurements.
If replicates are available, it is sensible to use the mean of the
replicates to estimate average bias. However, when estimating the limits of agreement,
the reduction in the standard deviation due to averaging of the measurements must be
considered and adjusted for if necessary.
The mean difference estimate is 6.0, which indicates that the Mini Wright meter reads
on average 6.0 l/min higher than the Wright meter. The confidence interval is
narrower because the measurement error was reduced by using the mean of the
(click to enlarge)
The limits of agreement estimate an interval of -67.8 to 79.8, which indicates that
the Mini Wright meter may measure as much as 67.8 l/min below and 79.8 l/min above
the large meter. This would be unacceptable for clinical purposes. Again, the
confidence intervals are narrower due to the use of more measurements.