Changing sample fraction for non-random camera sites?

[Tristen Brush]

Hi Eric, sorry to be spamming this group lately (it's the time of reckoning for my first manuscript).

I'm wondering if you've ever heard of people adjusting their angle of view calculations to deal with non-random transect placement. For example, many of my cameras are facing game trails or even roads, where the probability of elk entering the viewshed is much higher than the probability that elk are, for instance, behind the camera.

When I include my sample fraction (currently 0.10) in the model, my estimates are astronomically high. I'm grappling with the fact that this might be because the microsites chosen for some cameras favour elk detections. On a grand scale, my cameras are on a grid with a random start point, but the exact placement typically coincides with some sort of habitat feature. In these cases, I think my 10% viewshed is representative of, say, 50% of the circle, but not the whole circle because elk probably aren't occurring in the other 50%.

Is there any precedent for adjusting the sample fraction to address this issue? If not, do you have any suggestions for reconciling this assumption violation?

Thanks a million,

Tristen

[Eric Rexstad]

Tristen

I understand your concern and the possible remedy you are considering. The usual answer to your dilemma is increased number of spatial replicates; however, you are past that point in your investigation.

I don't know of an objective way to account for microsite differences between stations. Perhaps others on the list might have some advice for you.

---

From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of Tristen Brush <teb...@gmail.com>
Sent: 04 February 2026 23:12
To: distance-sampling <distance...@googlegroups.com>
Subject: [distance-sampling] Changing sample fraction for non-random camera sites?

 

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