Bland-Altman 95 Limits of Agreement: An Introduction
The Bland-Altman 95 limits of agreement is a statistical method used to assess agreement between two sets of measurements. It was developed by Martin Bland and Douglas Altman in 1986 and has since become widely used in biomedical research and other fields.
The Bland-Altman 95 limits of agreement method involves plotting the differences between the two sets of measurements against their average. This produces a scatter plot, with the horizontal axis representing the average of the two measurements and the vertical axis representing the difference between them.
The limits of agreement are calculated by multiplying the standard deviation of the differences by 1.96 (which represents the 95% confidence interval) and adding and subtracting this value from the mean difference. This produces two lines on the scatter plot, known as the upper and lower limits of agreement.
The Bland-Altman 95 limits of agreement method is useful for assessing the degree of agreement between two sets of measurements, particularly when the measurements are continuous and not categorical. For example, it could be used to compare the readings from two different blood glucose monitors or to assess the agreement between two different methods of measuring blood pressure.
The method has several advantages over other methods commonly used to assess agreement, such as the correlation coefficient or the coefficient of variation. These measures only assess the strength of the relationship between the two sets of measurements, rather than the degree of agreement between them. In addition, the Bland-Altman 95 limits of agreement method allows for the detection of systematic bias in the measurements, which other methods may miss.
However, there are also some limitations to the Bland-Altman 95 limits of agreement method. One potential issue is that it assumes that the differences between the two sets of measurements are normally distributed, which may not always be the case. In addition, it may not be appropriate for assessing the agreement between measurements that have a non-linear relationship.
In conclusion, the Bland-Altman 95 limits of agreement method is a powerful tool for assessing agreement between two sets of continuous measurements. It is widely used in biomedical research and other fields, and has several advantages over other commonly used methods. However, it is important to be aware of the assumptions and limitations of the method, and to carefully consider whether it is the most appropriate tool for a given analysis.
