Method: Statsample::StratifiedSample.variance_esd_wor

Defined in:
lib/statsample/multiset.rb

.variance_esd_wor(es) ⇒ Object 



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# File 'lib/statsample/multiset.rb', line 138

def variance_esd_wor(es)
  n_total=calculate_n_total(es)
  sum=es.inject(0){|a,h|
    val=h['N']*(h['N']-h['n'])*(h['s']**2 / h['n'].to_f)
    a+val
  }
  (1.0/(n_total**2))*sum
end