wrong ttest result

[SterArcher]

Hi!

I wanted to compare two groups using ttest function.

The violin plot shows significant overlap, but the ttest from your package returns significant result.

pg.ttest(df["Skupina"], df["masa"])

           T  dof alternative     p-val         CI95%  cohen-d    BF10  \

T-test 3.828714 56 two-sided 0.000327 [0.16, 0.51] 1.00547 79.764

       power  

T-test 0.964251

When using scipy i get non-significant result.

# Perform t-test
group1 = df[df["Skupina"] == 1]["masa"]
group2 = df[df["Skupina"] == 2]["masa"]
t_stat, p_value = ttest_ind(group1, group2)

print(f"T-statistic: {t_stat}, P-value: {p_value}")

T-statistic: -1.2849905790443539, P-value: 0.20971011250741314

Why would that be? The latter result was also confirmed by another person in R.

Thank you!

[raphaelvallat]

Hi,

I believe that the correct code to replicate the SciPy result is:

import pingouin as pg
group1 = df[df["Skupina"] == 1]["masa"]
group2 = df[df["Skupina"] == 2]["masa"]
pg.ttest(group1, group2)

Alternatively, you can use:

import pingouin as pg
pg.pairwise_tests(data=df, dv="masa", between="Skupina")