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How to remove observer bias from grid based observations

ChenaySimms

Hi all

I have old animal sightings data that I want to analyse for distribution, frequency and landscape utilization. However the data was captured using a grid system where all animals seen within a specific grid cell get assigned the coordinate of the bottom left corner of the cell.

The area is fairly mountainous and there seems to be a strong bias towards grid cells with roads through them.

Is there a way to quantify and or remove this bias?

Any suggestions would be welcome.

Regards

Chenay

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ChenaySimms

Thanks for your comments, I will definitely look further into that aspect of it 🙂

I have a statistician helping with the analysis, I was just hoping that this data would lend itself to a more spatially based analysis.

BenLeslie1

I can't answer the question but you need to think carfully about the bias and what is causing it. Is it because there are more observers on the road or are the animals attracted to the roads, maybe by road-kill or litter. Do shubs/hedges/farms/houses line the roads are these a habitat for the animals? Do roads run through areas that are reletively flat and does this make them more habitable?

If you don't have these answers you may just have to accept that the data isn't good enough to tell you what you want. If you do have these answers you may need to employ a proper statistician to help you understand the data.

ChenaySimms

Sorry 🙂

Included here is the point data as well as the results of an identify of one of the points (you can see that this one point has 73 records associated with it). Below that is a quick density map using all the points with the roads overlayed on it. There roads to the south and west are the most frequently used roads whilst the roads to the east are used fairly infrequently. There seems to be a correlation between them and animal densities...... There is also some terrain bias but at first glance it is not as influential.

XanderBakker

I think Dan Patterson‌ refers to "A picture is worth a thousand words"... Can you include a screenshot of your data to show what we are taling about?

ChenaySimms

Hi Dan

No, the records are captured as points. The reserve was divided into a reference grid of 1 * 1km cells that were used to assign a location to the sightings (so one location was given to all the sightings within that grid).

I had thought of transforming the points to a raster but there are too many variables in the attribute table that I need to keep.

Thanks

Chenay

DanPatterson_Retired

Image?

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