Variance is a characteristic parameter of a probability distribution: it is not a statistic. In any particular situation (with a few strange exceptions) it has only one value and therefore cannot have any bias.
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The n-1 indicates that the calculation is being expanded from a sample of a population to the entire population. Bessel's correction(the use of n − 1 instead of n in the formula) is where n is the number of observations in a sample: it corrects the bias in the estimation of the population variance, and some (but not all) of the bias in the estimation of the population standard deviation. That is, when estimating the population variance and standard deviation from a sample when the population mean is unknown, the sample variance is a biased estimator of the population variance, and systematically underestimates it.
Favourable variance is that variance which is good for business while unfavourable variance is bad for business
the use of random sampling that results in an unbiased conclusion.
Variance is used to add standard deviations when comparing two samples or populations. Variance is simply Std^2. The formula for obtaining Std is dependent on the type of sample taken\ hypothesis test performed i.e. 2-proportion pop/sample, single proportion, poussin, binomial, etc.
There are 7 variances associated with a budget ( which are generally calculated for controlling purposes) 1- Material Price variance 2- Material Quantity variance 3- Labor rate variance 4- Labor efficiency variance 5- Spending variance 6- Efficiency variance 7- Capacity variance