[Openspace] LISA used in Geoda and ArcInfo

[Roger Bivand]

On Mon, 12 May 2008, Patrick Yang wrote:

> Hello everybody,
>
> Does any one have both experiences of computing LISA in Geoda and ArcInfo
> package of Spatial Statistic Tools. I ran the same set of areal data based
> on the same spatial weight matrix (the first order contiguity), but got very
> different outcomes:

Dear Patrick,

In situations like this, it really helps to provide example data (for 
instance a downloadable compressed archive file with the data files and 
screen shots of the two software systems showing the selected argument 
values). I'm sure you have checked every possibility that this is not a 
difference in your use of the software, but a difference in the software 
itself, but more eyes seeing your situation may see something that you 
have not thought of.

The key thing here is that the local Moran I values differ. This can come 
from three things: different data, different weights, and/or different 
software implementations. As both implementations are widely used, the 
community would benefit greatly if we could establish what is going on. In 
the Arc case, the Python code can be read if need be, but GeoDa local 
Moran's I values typically agree with the R spdep localmoran() function 
output for the same data and weights. In other words, GeoDa is pretty 
reliable, and indeed by the author of the original local Moran's I paper.

Can you provide a documented example showing the problem? Could you also 
please say which build of both implementation you are using - it may be 
something that has been fixed in a later release?

Once the local Moran's I values agree, other differences will be related 
to how any testing is carried out, and here there is more room for random 
differences (different random number streams in GeoDa itself can give 
slightly different results). So let's take this step by step.

Hope this helps,

Roger

>
> - most part of area are recoginized as low-low significally in Geoda, but as
> random process based on the Z-core (cut off by 1.96) in ArcInfo
> - There is no high-high combination in Geoda, but can find hot spots in
> ArcInfo
> - The caculated local Moran I is different in the two softwares
>
>
>
> Can anybody kindly help me to explain the reason? PS: I choose the
> standarized row for the weight matrix in ArcInfo but I guess in GeoDa it is
> the same configuration. if it is not so, please point it out. Any what other
> reasons? Thank you.
>
>
> Bests,
> Zhenshan
>
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no