Re: [R] correlation value and map

From: Jenny Barnes <jmb_at_mssl.ucl.ac.uk>
Date: Wed 10 Jan 2007 - 16:24:34 GMT


Hi Zoltan,

Right, I have 30x32=960 data points per year (It is actually the mean febuary precipitation total in case you were wondering) at each grid point over the world, so I have 960 data points each of the 43 years. Therefore can I do anything with a trend and residuals? I don't think I can if it's just mean feb precipitation, one data point per grid square per year... I apreicate your help though very much.....although I do still need to perform a spatial correlation if anyone else can help?

Many thanks,

Jenny

Hi Jenny!

So if i understand your datafile corect you have 960 case for a year. Any you have 43 years.. Yes?

I'm not sure you should use correlation in this situation because of the autocorrelation of the data. There are big autocorrelation on spatial data's like what you use, and there are also a very big autocorrelation in time series data. I think you have to decompose your time series, and you have to cut down, the trend (and maybe some kind of sesonality), and than for the residuals you should do a correlation. You have to filter out the autocorrelation on the spatial data too, some way..

And because of the above problems, don't calculate correlation for the entierly databases!

bye,
Zoltan



Jennifer Barnes
PhD student - long range drought prediction Climate Extremes
Department of Space and Climate Physics
University College London
Holmbury St Mary, Dorking
Surrey
RH5 6NT
01483 204149
07916 139187
Web: http://climate.mssl.ucl.ac.uk

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