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Because actual rather than absolute values of the forecast errors are used in the formula, positive and negative forecast errors can offset each other; as a result, the formula can be used as a measure of the bias in the forecasts. A disadvantage of this measure is that it is undefined whenever a single actual value is zero.
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Any non-linear differentiable function, (,), of two variables, and , can be expanded as + +. If we take the variance on both sides and use the formula [11] for the variance of a linear combination of variables (+) = + + (,), then we obtain | | + | | +, where is the standard deviation of the function , is the standard deviation of , is the standard deviation of and = is the ...
For processes that produce homogeneous batches (e.g., chemical) where repeat measurements vary primarily because of measurement error; The "chart" actually consists of a pair of charts: one, the individuals chart, displays the individual measured values; the other, the moving range chart, displays the difference from one point to the next.
For example, if the length measurement L was high by ten percent, then the estimate of g would also be high by ten percent. If the period T was under estimated by 20 percent, then the estimate of g would be over estimated by 40 percent (note the negative sign for the T term).
The binomial distribution is the basis for the p-chart and requires the following assumptions: [2]: 267 The probability of nonconformity p is the same for each unit; Each unit is independent of its predecessors or successors; The inspection procedure is the same for each sample and is carried out consistently from sample to sample
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For a confidence level, there is a corresponding confidence interval about the mean , that is, the interval [, +] within which values of should fall with probability . ...