gof_ds fails to produce the Q-Q plot

[Asier Rodríguez Larrinaga]

Hi, everyone,

I am fitting a point transect model, with four covariates and an hr detection function (no adjustments) and I cannot get the Q-Q plot from gof_ds.

Is there any particular situation where gof_ds does not produce the plot? Or, am I simply doing something wrong?

I found no comment of such an issue in the list (nor in other places).

I would appreciate any hint.

Cheers,

Asier

[Asier Rodríguez Larrinaga]

Sorry, I forgot to explain that, of course, I set plot=TRUE within gof_ds and I also tried with a simplified version of the model, without covariates.

Best regards,

Asier

[Eric Rexstad]

Asier

Thanks for your question. One of the facets of your study that you don't describe is the manner in which the data were recorded. Did you record exact radial distances to the detection, or did you record detection distances in bins (0-10, 10-20, ...)? If it was the former, you should obtain a QQ plot. If it was the latter (binned distances) QQ plots (and tests) will not be produced. QQ plots can only be created for exact distance data.

If you did record data as exact distances, gof_ds() should be able to produce a QQ plot; if that is the case, you might need to send your data and code off-line for further investigation.

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From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of Asier Rodríguez Larrinaga <asi...@gmail.com>
Sent: 06 April 2025 10:26
To: distance-sampling <distance...@googlegroups.com>
Subject: [distance-sampling] gof_ds fails to produce the Q-Q plot

 

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[Asier Rodríguez Larrinaga]

Hi, Eric.

Thanks a lot for your quick response. Well, I did not know that Q-Q plot is not possible with binned distances, although it sounds reasonable now that I know. In fact, my data are entered as exact distances, but I am modelling through 4 20-m bins, by means of the "cutpoints!" option. Is this the reason why it does not plot a Q-Q plot?

Best regards,

Asier

[Eric R]

Yes, that's the reason for no QQ plot. You have binned your data before fitting the detection function model; hence no QQ plot.