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Industrial Statistics with Minitab by Xavier Tort-Martorell Llabres, Lluis Marco Almagro, Pere Grima Cintas

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9.3 Normality Test

To apply this test to the data of the detergent's weights presented before, go to: Stat > Basic Statistics > Normality Test

ch09fig010.eps

If the data come from a normal distribution, the values of their cumulative proportions will form approximately a straight line on a normal probability plot.

ch09fig011.eps

An alternative way to carry out the normality test is the following.

Graph > Probability Plot: Single

ch09fig012.eps

Notice that it is possible to fit other distributions. According to the chosen distribution, its parameters may be entered; however, this is optional as by default they are automatically estimated from the data.

ch09fig013.eps

If the points lie within the confidence bands, it can be assumed that the values come from the distribution under study using a confidence level of 95%. This level can be changed in tab Data Display, the option which is found next to the Distribution tab.

If only few data are available, which is equivalent to having little information, the hypothesis that the data come ...

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