Hypothesis Testing
Null hypothesis, p-value, t-test, chi-square test with scipy.stats.
What is a Hypothesis Test?
A hypothesis test uses data to decide whether an observed effect is real or just random chance. It is how data scientists justify claims like "the new design increased clicks".
Null vs Alternative
The null hypothesis H0 says there is NO effect (the default, skeptical position). The alternative H1 says there IS an effect. We try to gather evidence against H0.