Hi Janda88,

Since you're mentioning this issue, let me try to tell you more about this.

The probability of type 1 error is just exactly equal to the significance level (call it alpha as usual). So we can manipulate it easily as we like. If one feels like, for just any reason suits, to take a higher risk of committing it, he/she just simply choose alpha equal to 10%. If he/she doesn't feel like it, just decreases the choice to 1% or even lower.

But this's not that easy in case of type 2 error.

The probability of type 2 error (call it beta as usual) will increase if we decrease alpha, and vice versa. But by how much? It depends on what is the true answer of the unknown parameter you're testing. In other words, beta is a function of the unknown parameter.

If we know the equation of this function as well as the true answer of the unknown parameter, we surely can calculate the exact answer of beta. But this is rarely the case in reality. And this means we don't know how much risk we're taking when talking about the possibility of committing a type 2 error.

That's why people tend to say "not reject the null hypothesis" but not "accept the null hypothesis".

If you accept it, you will immediately expose to the risk of committing type 2 error, and people don't like to take this risk because they don't know the probability of the risk.

But if you're just not rejecting it, you can make some excuse saying "not rejecting it doesn't mean accepting it", something like that. Then you can even further say "we need further investigation in order to determine whether we should really accept it or not". This is a game of language.

But in some cases, people just gotta really accept the null hypothesis, especially when they gotta make a decision and take an action upon it (if you're asking me what's the reason, well, I don't know either). One word, "just do it!"

In this case, either they pay some money or time or resources or any other costs to make "further investigation in order to determine...", or they can only "just do it!"

Hope the comment helps your understanding.

## Stay connected