Blame statistics/ttest_source.c

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/* statistics/ttest_source.c
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 * 
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 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 Jim Davies, Brian Gough
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 * 
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 * This program is free software; you can redistribute it and/or modify
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 * it under the terms of the GNU General Public License as published by
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 * the Free Software Foundation; either version 3 of the License, or (at
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 * your option) any later version.
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 * 
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 * This program is distributed in the hope that it will be useful, but
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 * WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * General Public License for more details.
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 * 
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 * You should have received a copy of the GNU General Public License
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 * along with this program; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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 */
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double 
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FUNCTION(gsl_stats,ttest) (const BASE data1[], 
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                           const size_t stride1, const size_t n1, 
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                           const BASE data2[],
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                           const size_t stride2, const size_t n2)
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{
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  /* runs a t-test between two datasets representing independent
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     samples. Tests to see if the difference between means of the
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     samples is different from zero */
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  /* find means for the two samples */
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  const double mean1 = FUNCTION(gsl_stats,mean) (data1, stride1, n1);
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  const double mean2 = FUNCTION(gsl_stats,mean) (data2, stride2, n2);
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  /* find pooled variance for the two samples */
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  const double pv = FUNCTION(gsl_stats,pvariance) (data1, stride1, n1, data2, stride2, n2);
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  /* calculate the t statistic */
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  const double t = (mean1 - mean2) / (sqrt (pv * ((1.0 / n1) + (1.0 / n2))));
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  return t;
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}
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