dht2 for stratified abundance estimates derived from mrds model

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Evan Curtis

Nov 22, 2021, 11:03:38 PM11/22/21
to distance-sampling
Hi all,

I have mark-recapture distance-sampling aerial survey data temporally stratified within a region of interest. Specifically, there are 12 replicate surveys within the 1 region of interest. Each replicate survey has 4 transects.
I've identified the following mrds ddf() model:

  mrmodel=~glm(~obsname + size),

I want to derive abundance and variance estimates with respect to each replicate survey using the ddf() model outlined above. I use dht2():

FG.roo.MRDS <- dht2(ddf = MRDS.6a,
                    flatfile = flatfile.mrds,
                    stratification = "effort_sum",
                    strat_formula = ~Rep,
                    er_est = "R2",
                    ci_width = 0.95)

my flatfile contains all five essential columns + the three covariates used in the mrds model. The error I can't get past when running the dht2() model is:

Error in if (ddf$ds$aux$point) "point" else "line" : 
  argument is of length zero

I'm uncertain about where or how to actually specify this information when using ddf(). There are two things I could think of that could be causing the error...

1. My ddf() model does have a similar ?'slot'? but it's address is:

2. There are duplicate observations in the flatfile (because observer name is a covariate and it is a mark-recapture model).

All suggestions much appreciated. Thanks in advance!


Eric Rexstad

Nov 23, 2021, 3:19:26 AM11/23/21
to distance-sampling, Evan Curtis

My suspicion about your error message is that dht2​ hasn't been tested with an object containing an mrmodel​ component.  You have already done the detective work to deduce when the dht2​ code goes looking for ddf$ds$aux$point​ it fails to find it.  As you note, the item of interest is in a different location.  Simply toy example (in addition to yours):

region <- book.tee.data$book.tee.region
egdata <- book.tee.data$book.tee.dataframe
samples <- book.tee.data$book.tee.samples
obs <- book.tee.data$book.tee.obs
# fit an independent observer model with point independence
result.io <- ddf(dsmodel=~cds(key = "hn"), mrmodel=~glm(~distance),
                 data=egdata, method="io", meta.data=list(width=4))

For now, dht2​ is not usable with models that include an mrmodel​ component.

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Sent: 23 November 2021 04:03
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Subject: [distance-sampling] dht2 for stratified abundance estimates derived from mrds model
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Evan Curtis

Nov 23, 2021, 3:02:18 PM11/23/21
to distance-sampling
Thanks once again Eric! 
I'll explore a different analysis option for the mrds replicates.


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