The ratio of H1 Variance to H0The variance that the test should discover.
For example, ratio=1.1, right-tailed, means that the test will identify variance that is greater by 10% from the null assumption.">Ratio Var1/Var0:
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Target: To check if the assumed variance ()σ20) is statistically correct, based on a sample variance S2.
the default is right tailed test, usually you worried only if the standard deviation is bigger then the expected one.
1. Right tailed example:
A factory uses machine to create screws. the standard deviation of the screws diameter must not exceed 0.1 mm.
2. Two tailed test example:
A factory uses a machine to create screws. recently the engineers upgraded a big module in the machine.
The quality assurance are interested to know if there was a change in the standard deviation of the screws diameter.
If the standard deviation is bigger the engineer must fix it to meet the expected quality.
if the standard deviation is smaller, sales may consider to sell screws with better standard, and higher price. Example1: A farmer calculated last year the variance of the apples' weight in his apple orchard σ20 equals 2 kg2, based on big sample
Current year he checked a small sample of apples and the sample variance S2 equals 3 kg2
Was the variance of the apple's weight changed this year?
The farmer will run the two-tailed test.
The farmer consulted with a statistician and told him that he only worry if the variance will be greater, smaller variance is not a concern.
The statistician recommend him to run the right-tailed test and check the H1: &σ2>2kg
|The population expected variance is known|
|Sample standard deviation|
The following R code should produce the same results:The R code doesn't exclude outliers.
1. Two-tailed test
A farmer calculated last year the average of the apples' weight in his apple orchard μ0 equals 17 kg, based on the entire population.
The current year he checked a small sample of apples and the sample average x̄ equals 18 kg
Has the average of the apple's weight changed this year?
The farmer calculates the sample standard deviation of the apple's weight.
2. Left-tailed test.
In the same example as above, the farmer only cares to know if the entire average is lesser this year.