Date:         Mon, 18 Oct 2010 15:03:26 -0400
Reply-To:     peterflomconsulting@mindspring.com
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Peter Flom <peterflomconsulting@MINDSPRING.COM>
Subject:      Re: How to create a jackknife macro
Comments: To: Keith Larson <keith.larson@ZOOEKOL.LU.SE>
In-Reply-To:  <AANLkTi=2OvB7BgQ-DFgJg5nSQdZ-nku+mY=HisXF55tp@mail.gmail.com>
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I am pretty sure that the by-now classic paper Don't Be Loopy by David
Cassell will show you how to do this.

The 'L isn't quite the same without the Casse 'L

Peter

-----Original Message-----
From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of Keith
Larson
Sent: Monday, October 18, 2010 2:25 PM
To: SAS-L@LISTSERV.UGA.EDU
Subject: How to create a jackknife macro

Dear list,

I have two species ranges determined from observations. Within each
range I have generated 1000 random points. I then extracted
environmental data for each observed and random point using GIS. Next,
I created a PCA of the environmental variable for all of the observed
and random points (both species). For the actual observed (not random
points), I then calculated the (absolute) difference for the mean of
each PC(1 to 4) between the two species. For example mean(PC1 for
species A) - mean(PC1 for species B), and so on for each PC(1 to4).

I would like to do the same for the random points (species A random
points, species B random points), but instead of a simple difference
using all of the random samples for each species, I would like to run
a jackknife, calculating the mean value 1000 times, subsampling the
data without replacement (jackknife), using 75% of the data for each
replicate. Once I calcuate these mean values, I would like to
calculate a 95% range on each PC.

Any help is VERY much appreciated.

Cheers,
Keith

A sample dataset might look like:

DATA Survey;
     INPUT Species PC1 PC2 PC3 PC4 ;
     DATALINES;
Species PC1 PC2 PC3 PC4
A_Obs 118 39 25 229
A_Obs 96 28 27 320
A_Obs 97 35 30 279
A_Obs 93 27 26 269
A_Obs 119 15 31 232
A_Random 105 11 31 259
A_Random 118 25 36 294
A_Random 104 30 29 310
A_Random 99 10 27 270
A_Random 91 19 34 322
B_Obs 91 22 32 276
B_Obs 120 38 37 315
B_Obs 114 35 25 290
B_Obs 98 30 27 281
B_Obs 98 36 29 322
B_Random 105 19 27 319
B_Random 104 15 32 292
B_Random 102 35 24 254
B_Random 104 23 27 285
B_Random 102 38 29 216;
RUN;

**************************************
Keith Larson, PhD Student
Animal Ecology, Lund University
Sölvegatan 37
223 62 LUND
Sweden
Phone: +46 (0)46 2229014
Mobile: +46 (0)73 0465016
Fax: +46 (0)46 2224716
Skype: sternacaspia
FB: keith.w.larson@gmail.com
**************************************