# Hypothesis Testing

#### stats1357

##### New Member
I was asked a valid question that I couldn't answer. Why perform Hypothesis Testing when I have the entire population data?

#### Dragan

##### Super Moderator
How do you define "entire population data?"

For example, suppose I want to prove that "All Crows are Black."

Next, a thought experiment. Suppose tomorrow I inspect every single crow around the world and I find that indeed every crow was in fact black.

Question: Have I proved that "All Crows are Black."

Answer: No, I have not. The reason is because I did not inspect all crows that existed previously and all crows that would exist in the future, which I cannot do. In short, I do not have the "entire population."

Thus, the need for Hypothesis testing, which is essentially based on what is referred to in logic as Modus tollens i.e. proof by contradiction.