# Plotting probability plot by hand

• level1
In summary, the conversation discusses how to plot a probability plot by hand without using statistical software. An example is also provided for plotting a probability plot to determine if a set of data is normally distributed. The conversation also mentions the use of q-q plots and the calculation of rank-based z scores for the y-axis.
level1
Anyone knows how to plot a simple probability plot by hand (manually) without using statisical software?

Can you give an example?
Because now your question is very general, and also very personal (some people will say they can, others won't).

Hi,

the example goes something like this:
Assuming a set of data is collected to show warping of a long metal pipe.

0.756 0.856 0.943 0.978 1.12 1.23 1.45 1.67 1.87

Plot a probability plot to ascertain if the data is of normal distribution.

I know how to use minitab to plot the probability plot and then check if it is
more or less a straight line or is there any out-lier.

But I would like to learn how to manually plot a probability plot.
Normally a graph plot will require 2 set of datas, 1 set for the x-axis and the other set for the Y-axis. But now that I have only 1 set of data, how to I use this particular set of data to generate the other set of data for the other axis?

Is there any standard parameters for the x-axis and y-axis?

The textbook says something about using percentile to calculate but I don't really understand what its trying to say... :(

I can see you are on the right track. What you are looking for is called qq plot. The way to tell if the data is normally distributed just by plotting their quantiles.
you have observed value as x values. you need rank based z score for the y axis.
http://www.stattucino.com/berrie/graphs.html

Last edited by a moderator:

## What is a probability plot?

A probability plot is a graphical representation of the probability distribution of a dataset. It is used to visualize how the data is distributed and to determine if it follows a particular probability distribution.

## Why is it important to plot probability by hand?

Plotting probability by hand is important because it allows for a better understanding of the data and the underlying probability distribution. It also helps in identifying any outliers or unusual data points that may affect the analysis.

## What are the steps for plotting probability by hand?

The steps for plotting probability by hand include:

• Sorting the data in ascending order
• Calculating the cumulative probabilities for each data point
• Plotting the data points against their corresponding cumulative probabilities on a graph
• Drawing a line through the points to create a smooth curve

## What are some common probability distributions used in probability plots?

Some common probability distributions used in probability plots include the normal distribution, exponential distribution, and Weibull distribution. These distributions are often used to model real-world phenomena and can provide insights into the data.

## Are there any limitations to plotting probability by hand?

Yes, there are some limitations to plotting probability by hand. It can be time-consuming and prone to human error. It may also not be suitable for large datasets or datasets with complex distributions. In these cases, it may be better to use statistical software for plotting probability.

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