Is estimated "D=13.422" in this picture the last population density?

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xiangjun zhou

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May 2, 2022, 11:51:23 PMMay 2
to distance-sampling
1.jpg
but I also saw another calculation method of populaition density, which is 
2.jpg
when I calculated density using above method, I found  the results were total different. the detail was as follows:
3.jpg
form this picture,we can acquired “f(0)=  0.67635E-01 ” ,so D=93*0.67635E-01/(2*124.602)=0.02524, 93 is animal quantity, 124.602 is total L, I want to know why and its reaon?thank  a  lot

xiangjun zhou

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May 3, 2022, 2:57:09 AMMay 3
to distance-sampling
animal population density was 13.422 or 0.02524,I want  to why these results are quite different? thanks

Stephen Buckland

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May 3, 2022, 4:29:35 AMMay 3
to xiangjun zhou, distance-sampling

Impossible to tell, from the information you provide, but you indicated your animals can be in groups.  Then, n is not the number of animals detected, but the number of groups.  You also need to multiply by estimated mean group size in the population.  (Using the default methods in the software, this isn’t simply the mean size of groups detected, because there is usually bias with larger groups being more detectable.)  You also have to take care that you’re working with the same units as the software, e.g. with area as hectares.

 

Steve

 

From: distance...@googlegroups.com <distance...@googlegroups.com> On Behalf Of xiangjun zhou
Sent: 03 May 2022 07:57
To: distance-sampling <distance...@googlegroups.com>
Subject: {Suspected Spam} [distance-sampling] Re: Is estimated "D=13.422" in this picture the last population density?

 

animal population density was 13.422 or 0.02524I want  to why these results are quite different? thanks

202253日星期二 UTC+8 11:51:23<xiangjun zhou> 写道:


but I also saw another calculation method of populaition density, which is 

when I calculated density using above method, I found  the results were total different. the detail was as follows:

form this picture,we can acquired “f(0)=  0.67635E-01 ” ,so D=93*0.67635E-01/(2*124.602)=0.02524, 93 is animal quantity, 124.602 is total L, I want to know why and its reaon?thank  a  lot

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Eric Rexstad

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May 4, 2022, 1:32:45 AMMay 4
to xiangjun zhou, distance-sampling
I cannot address the density estimate of 13.422 because I don't know how it was derived.  But the two estimators of density you present are equivalent.  You can see from the formulas that mu-hat (shown as ESW in computer output) is the reciprocal of f(0)-hat.

Looking at the second screen capture, you see the output shows f(0)=0.067635 and ESW=14.785 (they are reciprocals).

  1. Using the values you provide for number of detections (93) and line length (124.602), the same value of D-hat is produced from both of the formulas.
Have you examined the online materials we have available at this web site?

Teaching distance sampling through video lectures and computer exercises.



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xiangjun zhou

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May 4, 2022, 2:05:26 AMMay 4
to distance-sampling
13.422/km2 was acquired by distance sampling software, but according to  formulas of second screen capture, we can calculate density =0.02524. my question is: which is right

Eric Rexstad

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May 4, 2022, 2:05:56 AMMay 4
to xiangjun zhou, distance-sampling
Seeing your data file was helpful.  Please sort your data such that all detections made on a transect are together.  In the file should first be all detections on transect 1, then all detections on transect 2, until the last transect.

Sent: 03 May 2022 09:36
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Subject: {Suspected Spam} Re: {Suspected Spam} [distance-sampling] Re: Is estimated "D=13.422" in this picture the last population density?
 
Length units is km, and   Distance units is m, could you help me with my data attached, and  finally telle me the result of population density, thank you

xiangjun zhou

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May 4, 2022, 2:10:55 AMMay 4
to distance-sampling
my data file   was right. I was confused by why anmal density from software and from formulas were different

Eric Rexstad

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May 4, 2022, 2:24:09 AMMay 4
to xiangjun zhou, distance-sampling
I'm afraid your data file is not correct.  I find the file contains 48 detections, not 93.  When I sort the file to bring together detections from a given transect, I find the transect lengths do not match.  For example, there were 4 detections on "line 28", but there are three different transect lengths associated with that transect

Likewise two different lengths for transect "29".

Please look through the example data sets provided in the Sample Projects directory of the Distance for Windows to see how data needs to be organised for analysis.


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xiangjun zhou

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May 4, 2022, 2:24:13 AMMay 4
to distance-sampling
I deliver my data in another posts, please help me confirm which is the right animal density and why density from distance software was different from  the  formulas calculation,thanks a lot

在2022年5月4日星期三 UTC+8 14:05:56<Eric Rexstad> 写道:

xiangjun zhou

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May 4, 2022, 4:37:22 AMMay 4
to distance-sampling
thanks a lot, I now understand it,thank you a lot ,you are a good person, wish you good day
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