Mean -----. Mean Mean 2SD ,8 Average vcr by long and short axes Fig 4. Mean VCf by long and short axis measurements Fig 5 shows the log-transformed data of fig 4. This still shows a relation between the difference and the mean VCF, but there is some improvement. The mean difference is 0.003 on the log scale and the limits of agreement are -0.098 and 0.106.However, although there is only negligible bias, the limits of agreement have somehow to be related to the original scale of measurement. If we take the antilogs of these limits, we get 0. 80 and 1.27 However, the antilog of the difference between two values on a log scale is a dimensionless ratio. The limits tell us that for about 95% of cases the short axis measurement of vcf will be between 0.80 and 1. 27 times the long axis VCF. Thus the short axis measurement may differ from the long axis measurement by 20% below to 27% above. (The log transformation is the only transformation giving back-transformed differences which are easy to interpret and we do not recommend the use of any other in this context. Mean 2sD 0 ---Mea∩ g 8 一.1 Mean 25D Average log vcf by long and short axes Fig 5. Data of fig 4 after logarithmic transformation. i These numbers were incorrectly printed as 0.008, -0.226, and 0.243 in the Lancet. This mistake arose because when revising the paper we dithered over whether to use natural logs or logs to base 10 and got hopelessly confused6 Fig 4. Mean VCF by long and short axis measurements. Fig 5 shows the log-transformed data of fig 4. This still shows a relation between the difference and the mean VCF, but there is some improvement. The mean difference is 0.003 † on the log scale and the limits of agreement are - 0.098 † and 0.106.† However, although there is only negligible bias, the limits of agreement have somehow to be related to the original scale of measurement. If we take the antilogs of these limits, we get 0.80 and 1.27. However, the antilog of the difference between two values on a log scale is a dimensionless ratio. The limits tell us that for about 95% of cases the short axis measurement of VCF will be between 0.80 and 1.27 times the long axis VCF. Thus the short axis measurement may differ from the long axis measurement by 20% below to 27% above. (The log transformation is the only transformation giving back-transformed differences which are easy to interpret, and we do not recommend the use of any other in this context.) Fig 5. Data of fig 4 after logarithmic transformation. † These numbers were incorrectly printed as 0.008, -0.226, and 0.243 in the Lancet. This mistake arose because when revising the paper we dithered over whether to use natural logs or logs to base 10 and got hopelessly confused