Clinical agreement in quantitative measurements

With advances in medical technology, simpler and safer methods for diagnosis and therapy are increasingly replacing the old ones and it has become important that these be correctly assessed. When a measurement by a new method is the same as that using the old method, one frequently encounters the problem of assessing the agreement. Evidence such as a correlation equal to 1 or equality of means is known to be inadequate. However, two recent approaches- limits of agreement and intraclass correlation coefficient- have gained acceptance but each has its own merits and demerits. To help investigators choose a procedure which is appropriate and to help them use it properly, we provide a description of these two approaches and discuss their advantages and disadvantages, both clinical and statistical, using a real example