Effective Strip Width from R package

[Stephanie CCF]

Hi all, 

I am new to Distance sampling analysis but since I obtain very different results between the R package and the standalone Windows used software, I'd like to have a way to extract the Effective Strip Width from R as it's not in the standard output.

Can someone help with this?

Thanks a lot for your help!

Stephanie

[Eric Rexstad]

Stephanie

The definition of effective strip (half) width (Buckland et al. 2015:10) is

you know your truncation distance (w) because you specify it either as maximum distance of a detection or your specified truncation distance. is provided as output labelled “average p”

Summary for distance analysis

Number of observations : 124
Distance range : 0 - 4 Model :
Half-normal key function AIC : 311.1385

Detection function parameters

Scale coefficient(s): estimate    se
(Intercept)           0.6632435 0.09981249

                      Estimate      SE             CV
Average p             0.5842744  0.04637627 0.07937413
N in covered region 212.2290462 20.85130509 0.09824906

so you can compute manually.

The message to the list dated 17Aug17 you quote (discrepancy) was caused by problems in data organisation; but do let us know what you uncover.

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[Stéphanie Périquet]

Dear Eric,

Thank you for your reply.
Am I correct is assuming that 2ESW=covered area/effort?

For the discrepancy between R and Distance standalone, was in my case due to the truncation distance not being set in the same way (someone else was using Distance and I was trying to compare with R results).
However, I did bump into another problem with Distance standalone, when the truncation "right truncate at largest observation distance" and then should be maximum distance of observation. It turns out that Distance truncates the distance anyway... (My maximum observation distance is 500m and Distance give me an ESW of 330m. Any idea what could cause that?


Thanks!
Stephanie

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[Eric Rexstad]

Stephanie

People customarily refer to ESW as if it was the width of covered strip from the transect out to the distance $\mu$.  Geometrically this is a half strip-width, but in the literature it goes by the designation of ESW.

You are not correct in your assertion that 2ESW=covered area/effort.  Covered area is 2wL where w is truncation distance and L is transect length.

ESW and truncation distance are not equivalent.  Here is the distinction between the two quantities as shown in Fig 5.3 of Buckland et al. (2015)

[Stéphanie Périquet]

Dear Eric,

Thanks for the figure, it does clarify things indeed.

Best,
Stephanie