
Evaluating uncertainty components: Type A A Type A evaluation of standard uncertainty may be based on any valid statistical method for treating data. Examples are calculating the standard deviation of the mean of a series of independent observations; using the method of least squares to fit a curve to data in order to estimate the parameters of the curve and their standard deviations; and carrying out an analysis of variance (ANOVA) in order to identify and quantify random effects in certain kinds of measurements. Mean and standard deviation As an example of a Type A evaluation, consider an input quantity X_{i }whose value is estimated from n independent observations X_{i ,k} of X_{i }obtained under the same conditions of measurement. In this case the input estimate x_{i }is usually the sample mean (4)
and the standard uncertainty u(x_{i}) to be associated with x_{i }is the estimated standard deviation of the mean (5)


