Calculate p_value in .paired_test like we do in .perform

estebanz01 · Apr 17, 2023 · 6918daa · 6918daa
1 parent 74f48b7
commit 6918daa
Showing 1 changed file with 7 additions and 3 deletions.
diff --git a/lib/statistics/statistical_test/t_test.rb b/lib/statistics/statistical_test/t_test.rb
@@ -74,10 +74,14 @@ def self.paired_test(alpha, tails, left_group, right_group)
 
  t_score = (differences.mean - 0)/down.to_r
 
- probability = Distribution::TStudent.new(degrees_of_freedom).cumulative_function(t_score)
+ t_distribution = Distribution::TStudent.new(degrees_of_freedom)
+ probability = t_distribution.cumulative_function(t_score)
 
- p_value = 1 - probability
- p_value *= 2 if tails == :two_tail
+ p_value = if tails == :two_tail
+ 2 * (1 - t_distribution.cumulative_function(t_score.abs))
+ else
+ 1 - probability
+ end
 
  { t_score: t_score,
  probability: probability,