[Task]: Q-Q plot and P-P plot discrepancy

[SachaEpskamp]

JASP Version

0.18.3

Commit ID

No response

JASP Module

Distributions

What analysis are you seeing the problem on?

Assess fit of distribution

What OS are you seeing the problem on?

macOS Silicon

Bug Description

Hi Jasp team! I am not sure if this is a bug or not, but I made a Q-Q plot and a P-P plot of a simple dataset in which I have the numbers 1-5 each 5 times. The Q-Q plot looks like this:

and the P-P plot like this:

Note that in the Q-Q plot, the sample quantiles are correclty put equal to the values with the same score (1s, 2s, etcetera), but the theoretical quantiles are instead ordered in a sequence. In the P-P plot this is the other way around, and now theoretical values that are equal are assigned the same cumulative probability but the sample values are ordered. Is this expected?

Here is a file that reproduces the plots:
QQ_PP_example.jasp.zip

Expected Behaviour

I am actually not sure what this should look like...

Steps to Reproduce

1. Type in a variable 1,1,1,1,1,2,2,2,2,2, etcetera
2. Distributions -> Uniform
3. Add variablea nd make the plots
   ...

Log (if any)

No response

More Debug Information

No response

Final Checklist

• I have included a screenshot showcasing the issue, if possible.
• I have included a JASP file (zipped) or data file that causes the crash/bug, if applicable.
• I have accurately described the bug, and steps to reproduce it.

[tomtomme]

confirmed with 0.19 flatpak

[JohnnyDoorn]

This seems to be the same behavior as SPSS (although the pattern is flipped because the axes are flipped).

Not that SPSS is a great example of course, but I guess that maybe @Kucharssim followed this convention?

[github-actions]

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