Why is the null hypothesis important?
What is meant by the null hypothesis?
When a null hypothesis is accepted and rejected?
Hey! Can someone explain to me in simple terms the definition of null hypothesis? If u can use an example it would be great! Also if we reject the null hypothesis does it mean that the alternative hypothesis is true?
I apologize as I'm probably misunderstanding something fundamental here.
My understanding is that the p-value is the sum of the probabilities of observing:
-
The outcome predicted by your hypothesis.
-
Any outcome that is equally rare or more rare.
Let's say I have the hypothesis that my coin is biased in such a way that over the next 20 flips, I will get precisely this outcome: HTHTHHHTTTTTHHTHTTHT.
The null hypothesis is that actually it's just a normal fair coin.
The odds of observing the outcome predicted by my hypothesis if the coin is actually a fair coin is 1 out of 220 .
The following outcomes are equally rare:
-
Getting precisely the outcome HHHHHHHHHHHHHHHHHHHH.
-
Getting precisely the outcome HHHHHHHHHHHHHHHHHHHT.
-
Getting precisely the outcome HHHHHHHHHHHHHHHHHHTH.
-
Getting precisely the outcome HHHHHHHHHHHHHHHHHHTT.
-
etc.
In fact, every single outcome of this precision is equally likely, so the sum of all these probabilities would be 1, so my p-value would be 1?
And now let's say I decide to proceed with my experiment anyway, and I flip the coin 20 times, and lo and behold, I do end up getting precisely the predicted outcome of HTHTHHHTTTTTHHTHTTHT.
Intuitively, it seems like the result of this experiment is extremely strong evidence in favor of the hypothesis, but given a p-value of 1, which is greater than 0.05, it seems like I would have failed to reject the null hypothesis.
And it seems like this problem would occur any time your hypothesis is so specific that it picks out one atomic outcome (as opposed to trying to group together related outcomes) out of all possible outcomes.

