any current errors associated with dht2 effort_sum stratification

[Janet Mossman]

Hi All,

I'm currently doing an analysis with line transect cetacean data in which we are calculating seasonal abundances for two geographic strata for three species. We have nine surveys completed in different months of the year with very different amounts of effort for each month. I would like to use all pooled data by species for the detection functions and then subset the data for each species by area and season and stratify in dht2 using effort_sum = month to account for the variation in effort by month. We are under a time crunch and I know there were errors in the past with how the variance (ER) was calculated in past versions of distance using effort_sum. I'm hoping someone can confirm that these errors have been corrected without me digging to far into the github. 

Thanks for any help or clarification you can provide. 

Janet Mossman 

[Eric Rexstad]

Janet

This is a stratification option that is seldom exercised so I can't swear that all daemons have been exorcised from this section of code.

I've done a scan of our Github issues for occurrences of "effort_sum". I see no mention of it in any open issues. Most activity around this dates back to June 2021, when there were several code modifications and the issue was closed. This form of stratification was disabled in December 2022 when used in conjunction with multiple detection functions.

My memory does not bring to mind any more recent discussions or activity regarding "effort_sum".

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From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of Janet Mossman <pacif...@gmail.com>
Sent: 03 February 2026 22:54
To: distance-sampling <distance...@googlegroups.com>
Subject: [distance-sampling] any current errors associated with dht2 effort_sum stratification

 

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[Janet Mossman]

Thanks for the reply Eric, perhaps we should stick with the tried and true geographic stratification- the survey was designed with equal coverage probability for the entire study area but weather resulted in differing amounts of effort per survey. We do not have enough replicates when split by season to use this strat option. I'm wondering why effort_sum is used so infrequently? 

Thanks,

Janet

[Eric Rexstad]

Janet

I suspect the reason "effort_sum" is a little-used method of stratification rests with us. There is little documentation on this approach within the R package and the description in the DistWin manual is a bit vague. Section 3.7.1 of Buckland et al. (2001) is also of little help.

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From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of Janet Mossman <pacif...@gmail.com>

Sent: 04 February 2026 17:46
To: distance-sampling <distance...@googlegroups.com>
Subject: Re: [distance-sampling] any current errors associated with dht2 effort_sum stratification

 

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