About normal probability paper
Probability paper stretches the Y axis by the inverse normal distribution, so a normally distributed sample falls on a straight line. Plot cumulative percentages against the measured value, read the mean off the 50% line and take the standard deviation from the slope. It is the classic hand method for checking whether data is normal.
The Y axis is stretched by the inverse normal (probit) function, so a normally distributed sample plots as a straight line. Plot cumulative percentage against the measured value, read the mean off the 50% line and estimate the standard deviation from the slope.
It is the classic pencil-and-paper normality check and still handy for reliability and particle-size work. A clear bend away from the line flags skew or a non-normal distribution at a glance.
Great for
- Checking data for normality
- Reliability and life-data plots
- Particle size distributions
- Quality control and process capability
Common questions
How do I check normality with this paper?
Plot your cumulative percentages against the values; if the points fall roughly on a straight line, the data is close to normal.
Where do I read the mean and standard deviation?
The value at the 50% line is the mean, and the slope of the fitted line gives the standard deviation.
Guides for this paper
Printing at the right size
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