I'm studying statistics from the book "design of experiments" by Montgomery and about the t-test it's stated it is necessary to check the samples are described by a normal distribution throughout a normal probability plot and I have noticed the y-scale is not familiar to me, it's neither linear of logaritmic. In the book is written:(adsbygoogle = window.adsbygoogle || []).push({});

the cumulative frequency scale has been arranged so that if the hypothesized distribution adequately describes the data, the plotted points will fall approximately along a straight line; if the plotted points deviate signiﬁcantly from a straight line, the hypothesized model is not appropriate. Usually, the determination of

whether or not the data plot as a straight line is subjective.

How is the yscale chosen?

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# T-test: normal probability plot

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