The Hippopotamus and His Hypothesis
There's a hippopotamus.
He's got a hypothesis.
His null specifies a parameter,
That he's still skinny, no change in his diameter.
And if there is a change, that he's gotten fat from all those fries,
Well that's his alternative, a deviation from his hypothesized size.
Hoping for the best, he checks his p-value,
The probability of having extreme data, if the null is true.
Because his p-value is small, he comes to realize,
He needs to reject his null, and start to exercise.
But when he weighs himself, he soon comes to see,
That there was a type 1 error and he really is skinny.
His null was really true, but he had rejected it,
Because his p-value was below threshold and therefore statistically significant.
But was the change practically significant? He didn't think so.
For a tonne-weighing hippopotamus, a 10 pound change is too low.
So although weighing a tonne may not be skinny for me or you,
The hippopotamus thought so and shouted "Yoohoo!"