If SD=6, mean =24, and CV =25% we can write: This is shown with the following example: I think we would agree that by definition CV is the standard deviation divided by the mean and that and that for precision we usually express it as a percentage, however, it could also be expressed as a ratio. Would you look at my example below and give me your comments/ feedback? There seems to be confusion in the field about the nomenclature for CV and how it is expressed in a formulas. Since the intra- and inter-assay CVs are less than 10% and 15%, respectively, this indicates a low amount of variation between measurements. This is an indication for the variation for the same readings on different plates:Īs you can see, the intra-assay CV is much lower than the inter-assay CV. This is the variation of measurements from the same plate (between readings 1, 2 and 3):įinally, we can work out the inter-assay CV between the mean values from the three plates. We then use the CV formula above in Excel to calculate the intra-assay CV for each plate. Here is our data:įirst, calculate the mean (average) between the readings 1-3 on each plate: We measured the same sample three times on a plate and on three different plates (Plates 1, 2 and 3). Imagine we have just performed an enzyme linked immunosorbent assay (ELISA) to calculate the concentration of protein X from the same plasma sample. Let’s go through an example to understand the calculation better.
#How to fine coefficient of varation minitab 18 series
Just chane ‘Values’ to your number series of interest: =(STDEV(Values)/AVERAGE(Values))*100 Example of using the CV If you are using Microsoft Excel to work this out, you can use the following Excel formula. To calculate the CV, you need to know the mean and the standard deviation for a series of measures.
Usually the intra-assay CV value is lower than the inter-assay CV because the variation between runs is higher, than on the same run. Inter-assay CV values should ideally be less than 15%. For example, measuring a sample on one plate and the same sample on a separate plate. Inter-assay CV is the variation of the sample measurement on different runs. Intra-assay CV values should ideally be lower than 10%. For example, measuring a sample in duplicate or triplicate on the same plate. Intra-assay CV is the variation of the sample measurement in the same run. In terms of the CV for assays in the labs, there are two types: intra- and inter-assay CV. The CV is the expressed as a percentage to easily determine the variation of the assay. Within the lab, it is mainly used to determine how reliable assays are by determining the ratio of the standard deviation to the mean. The coefficient of variation (CV) is a measure of precision from repeated measures.
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