code: public static double runoffCoefficientError(double[] obs, double[] sim, double[] precip) {
          sameArrayLen(sim, obs, precip);
  
          double mean_pred = Stats.mean(sim);
          double mean_val = Stats.mean(obs);
          double mean_ppt = Stats.mean(precip);
          double error = Math.abs((mean_pred / mean_ppt) - (mean_val / mean_ppt));
          return Math.sqrt(error);
      }
docs: Runoff coefficient error ROCE
  
  @param obs
  @param sim
  @param precip
  @return