id_geno_checksum: GWAS overlap test without sharing genotypes



tutorial for a successful first run:

- change to a directory with a valid plink binary dataset (bed/bim/fam), for more details: http://pngu.mgh.harvard.edu/~purcell/plink/data.shtml#bed
- download the perl-script (id_geno_checksum.v1.0.2), 
     either with clicking on the link: 
          http://www.broadinstitute.org/~sripke/share_links/checksums_download
     or directly from the comandline: 
	  wget http://www.broadinstitute.org/~sripke/share_links/checksums_download/id_geno_checksum.v1.0.2
- make the perl script executable: e.g. 
          chmod u+x id_geno_checksum.v1.0.2
- download and unzip the helper files, e.g. directly from the comand line:
          wget http://www.broadinstitute.org/~sripke/share_links/checksums_download/CKS_batches_50_0114b.tar.gz
	  tar -xvf CKS_batches_50_0114b.tar.gz
- make sure the program plink is found and executable in the path (you can still define another location via options), e.g. try
          plink --help
	  if necessary you'll find pre-compiled version for direct download: http://pngu.mgh.harvard.edu/~purcell/plink/download.shtml

- run the program with (assuming the three files BFILE.bed, BFILE.bim and BFILE.fam are in your working directory)

          ./id_geno_checksum.v1.0.2 --bfile BFILE

- if run succesfully you will notified with a big success banner and asked to share a specific file with your collaborator
- for more details and options please use ./id_geno_checksum.v1.0.2 --help




here some further considerations:

- the script creates non identifiable checksum out of GWAS SNPs
- it uses ten batches with 50 SNPs each, all of them found on all current and older GWAS platforms I encountered yet (dating back to Affy500 and Illumina I317 up to the HumanCore).
    with genotype representation of 0,1,2 there are 3^50 = 7.1e23 possible different configurations within each batch
- it uses the <cksum> program as standardly available on UNIX platforms with 32 bit CRC algorithm
    with 2^32 = 4.3e10 possible distinct outomes
- this means for each distinct checksum there exist ~1.0e23 differnt possible genotype configurations
    this algorithm therefor does not provide a single key to the genotype configuration



** WARNING **: even though these checksums do not contain genotype information these are powerful identifiers.
  
   $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
   $$$$$$$  DO NOT POST CHECKSUMS on public websites or similar  $$$$$$$$$$$$$$$
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