Created
October 19, 2023 02:34
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2x2 table chi squared test ... use at your own risk ;)
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| require 'statistics2' | |
| def chisq_test(a, b, c, d) | |
| total = a + b + c + d | |
| row1_total = a + b | |
| row2_total = c + d | |
| col1_total = a + c | |
| col2_total = b + d | |
| e_a = (row1_total * col1_total).to_f / total | |
| e_b = (row1_total * col2_total).to_f / total | |
| e_c = (row2_total * col1_total).to_f / total | |
| e_d = (row2_total * col2_total).to_f / total | |
| chisq = | |
| ((a - e_a)**2 / e_a) + ((b - e_b)**2 / e_b) + ((c - e_c)**2 / e_c) + ((d - e_d)**2 / e_d) | |
| Statistics2.chi2_x(1, chisq) | |
| end | |
| pp chisq_test(0,2,3,4) # => 0.25683925795785645 | |
| pp chisq_test(1,2,3,4) # => 0.7781596861761657 | |
| pp chisq_test(10,20,30,40) # => 0.372998483613487 | |
| pp chisq_test(100,20,30,40) # => 7.044113736753843e-09 | |
| pp chisq_test(1000,20,30,40) # => 0.0 |
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