BlandAltmananalys

BlandAltmananalys is a statistical method used to assess the agreement between two measurement techniques or methods. It was developed by J. Martin Bland and Douglas G. Altman and is widely employed in fields such as medicine, engineering, and biology where comparing different ways of measuring the same quantity is common. The core idea is to visualize the difference between the two measurements for each subject against their average.

The analysis plots the difference between the two measurements on the y-axis and the average of the two measurements on the x-axis. This graphical representation allows for the identification of any systematic bias, where one method consistently over- or under-estimates the other, or proportional bias, where the difference between the methods increases with the magnitude of the measurements.

Key outputs of a BlandAltmananalys include the mean difference, which estimates the average bias, and the limits of agreement. The limits of agreement are typically calculated as the mean difference plus or minus 1.96 times the standard deviation of the differences. This range indicates the interval within which 95% of the differences are expected to lie. If the limits of agreement are too wide, it suggests that the two methods are not interchangeable for practical purposes. The analysis helps researchers determine if a new measurement method is a valid substitute for an existing one or if they can be used together.