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From |
Jochen Mistelbacher <jocsar@t-online.de> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Moran I and spatial correleation help needed |

Date |
Wed, 13 Feb 2008 19:34:31 +0100 |

Dear Recai,

I have not used the mentioned Stata-programs as yet, so can not say much about them. If I may, I would refer you to the freeware "GeoDa" developed by Luc Anselin and his team. However, for a specific diagnostic test of alternatives, lag or error, I think the command "spatdiag" is required.

Point 4) Depending on the outcomes of the diagnostic tests, I would just like to mention that:

-if the true model contains a lagged variable which would be ignored in OLS, the OLS estimators will be biased and inconsistent;

-if OLS is applied in the presence of residual spatial autocorrelation, parameter estimates will still be unbiased but inefficient, the standard asssumption of a spherical error covarinace matrix will fail to hold, so the performance of further tests might be seriously affected. So it is basically a problem of efficiency and inference.

Greetings,

Jochen

RECAI AYDIN wrote:

Dear users,

I am new in "spatial correlation" and need your help. I appreciate if you can help me. here are the commands I run and I have no problem getting the output. However, I cannot say it for the output:)

spatcorr value, bands(0 1.5 3 4.5) xcoord(x) ycoord(y)cumulative

spatwmat, name(W) standardize xcoord(x) ycoord(y) band(0 1.5)eigenval(E)

spatreg value sf sf2 age lot br fb pool d1 d2 d3 d4 d5, weights(W) eigenval(E) model(lag)

spatreg lnvalue sf sf2 age lot br fb pool d1 d2 d3 d4 d5, weights(W) eigenval(E) model(error)

My questions are:

1) I noticed that I can use only one variable after "spatcorr" and I assume it must be the dependent variable but that means the program is only checking for the spatial correlation in that variable alone without knowing what my full model is. That does not make sense to me. Then how does it determine if the spatial correlation is "lag" type or "error" type unless it defines the error as the deviation in Y?

2) I tried to run "spatcorr" with "lnvalue" as I normally use semi-log form and I got different Moran I. Can I use this command with transformed variable. How does that affect the interpretation of the I?

3) Is there any easy way of understanding if the spatial autocorrelation is due to "lag" or "error" from the output?

4) When I have the output for the last two lines (spatreg) and compare them with OLS, I do not see much difference even though Moran I, rho and lambda all are significant. How can I knoe that actually one is superior to the others. This last one is especially important for me. Because I really doubt about the importance of spatial autocorrelation and I need to be convinced by one of the "believers":).

Thank you for your time and attention and I look forward to hearing from you soon.

Recai

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**References**:**st: Moran I and spatial correleation help needed***From:*"RECAI AYDIN" <RECAI.AYDIN@lamar.edu>

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