The problem is about creating a Hypothesis Testing on the dataset that is divided between two groups: C1 and C2. In order to prove that taken Null Hypothesis is true, I've calculated: Mean, standard deriviation, number of test samples for each dataset, value of test statistic z, and finally: p-value. When it comes to the one-tail test, everything seems to be correct:
z = 0.22343
p-value = 0.4116
alpha = 0.05
so my null hypothesis is proven.
But whenever it comes to the two tail test, I do obtain something weird:
z = 3.97447
p-value = 7.05355
alpha = 0.02
As i do remember, p-value should be smaller than 1 and bigger than 0, so it is not correct. I do use almost identical formulas, except for p-value, that in the first example was calculated with the usage of:
p-value = F(-|z|)
in case of two tail test:
p-value = 2*F(-|z|)
Does anyone has a clue what is wrong?