odd behavior of TwoSamplesIndependent.probability_not_equal_variance

[fauman]

Seems to give incorrect value. For example:

a=[0,0,0,1,1,1,2,2,2].to_scale
b=[2,2,2,3,3,3,4,4,4].to_scale
t_2 = Statsample::Test::T::TwoSamplesIndependent.new(a,b)
t_2.probability_not_equal_variance

this gives the result: => 0.03333672278567579

However, the result should be: 0.00016053418045947065

Which actually is the value of t_2.probability_equal_variance

The issue seems to be with Distribution::T.cdf which treats df different if its a Fixnum vs a Float.

For the two vectors, where the variance actually is the same, the t statistic and the df should be the same for the equal_variance case and the not_equal_variance case.

But Distribution::T.cdf(-4.8990,16) doesn't give the same result as Distribution::T.cdf(-4.8990,16.0)

I only just started using statsample today, so I don't know if this is a new issue or a long-standing one.

[clbustos]

I can't replicate the result with ruby 1.9.3. Can you give me more information of your setup?

• Ruby version
• Distribution and statsample gem version

[fauman]

Ok - must just be me - I'll keep checking my set up.

I'm on Windows XP
Ruby 1.9.2-p180
statsample 1.0.1

I do not have statisics2 or gsl installed

I'm using NetBeans 6.9.1 to manage my Ruby Gems

[clbustos]

Should be the ruby code. I will close this issue and open one on Distribution gem.