Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page

Highlighted

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Jun 9, 2020 7:30 PM
(1154 views)

Hi,

Is there an option to view the probability plot when making a log-normal fit with a distribution analysis?

Thanks

2 ACCEPTED SOLUTIONS

Accepted Solutions

Highlighted

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Hi,

From the red hotspot of beside the name of your column in the Distribution platform choose "Continuous Fit -->Fit lognormal." Then, from red hotspot beside "Fitted Lognormal Distribution," choose "Diagnostic Plots." You then have the option of fitting the P-P and/or Q-Q plots. Is that what you're looking for?

Highlighted

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

@HadleyMyers provided you with a solution. However, if your lognormal distribution has a large mean and/or variance, the scaling on the QQ plot usually does not have the familiar custom probability plot that scales the Y axes like custom probability paper (yes I am showing my age, things we used pre graphical calculator/computer days).

I suggest you right click on the column of data you're fitting, select **Transform** and use **Log**, then **Continuous Fit > Fit Normal**.

Below is a screenshot of ** Analyze > Distribution > Continuous Fit > Fit Normal** of 100 random lognormal(4,2) values transformed with Log. The table with script is attached.

Another suggestsion is to use the QQ plot that Hadley suggested and click on the Y axis of he QQ plot and change Linear to Log.

4 REPLIES 4

Highlighted

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Hi,

From the red hotspot of beside the name of your column in the Distribution platform choose "Continuous Fit -->Fit lognormal." Then, from red hotspot beside "Fitted Lognormal Distribution," choose "Diagnostic Plots." You then have the option of fitting the P-P and/or Q-Q plots. Is that what you're looking for?

Highlighted

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

@HadleyMyers provided you with a solution. However, if your lognormal distribution has a large mean and/or variance, the scaling on the QQ plot usually does not have the familiar custom probability plot that scales the Y axes like custom probability paper (yes I am showing my age, things we used pre graphical calculator/computer days).

I suggest you right click on the column of data you're fitting, select **Transform** and use **Log**, then **Continuous Fit > Fit Normal**.

Below is a screenshot of ** Analyze > Distribution > Continuous Fit > Fit Normal** of 100 random lognormal(4,2) values transformed with Log. The table with script is attached.

Another suggestsion is to use the QQ plot that Hadley suggested and click on the Y axis of he QQ plot and change Linear to Log.

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Re: Probability plot for log-normal distribution fitting

Hi gzmorgan0,

I agree, making the log transformation is a great way to get the intervals on the plot too. I did this before but was also wondering about getting a plot for the log fit. The PP/QQ do a good job.

Thanks for the help.

I agree, making the log transformation is a great way to get the intervals on the plot too. I did this before but was also wondering about getting a plot for the log fit. The PP/QQ do a good job.

Thanks for the help.

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Get Direct Link
- Email to a Friend
- Report Inappropriate Content

Re: Probability plot for log-normal distribution fitting

Hi Hadley,

That is what I was looking for but without the confidence interval. But not a big deal.

Thanks for showing me around.

That is what I was looking for but without the confidence interval. But not a big deal.

Thanks for showing me around.