# Is my null hypothesis correct in this case?

I'm trying to understand the correct ways of expressing a null hypothesis. So I've created this case and I'd like to know if I'm on the right track.

Case 1: There is a general understanding that keeping a pot closed with a lid reduces the time taken to cook. This is because more heat is trapped in the pot. I (as a researcher) seem to have a different view that other factors such as the type of pot also matters. So I want to test if this is true and I'm going to test a number of different types of pots both with and without the lids on.

Null Hypothesis (I hope I'm correct here) : There is no difference is cooking time, whether or not the pot is covered

My question in this regard: I'm confused about the null hypothesis being the 'default' situation with 'no change'. So I also tend to think that the null hypothesis is the generally accepted condition that cooking with the lid on reduces cooking time.

So what is my correct null hypothesis?

• Your description of your case is ambiguous to me. It sounds like you want to determine if the type of pot has an effect of cooking time after having controlled for lid. Is that what you want to know? Or do you think that the lid is irrelevant to the cooking time? Or do you think that it is the type of pot that's relevant instead of the lid, & that other people were confused because they inappropriately looked at the lid in isolation? – gung Sep 27 '16 at 19:07
• Wow! @gung that's amazing, how you interpret that little para... After looking at your comment, I am clearer now. So I actually meant that the lid indeed has an effect, but not only that matters. However, the people have looked at only the lid in isolation. Perhaps as a result of testing the lid only, I may find that the lid really has no effect, and this may lead to further studying the type of pot as well... I hope that makes sense :) – itsols Sep 28 '16 at 1:51

• What do you mean by $H_0$-notation? – Bernhard Sep 28 '16 at 11:53
• Do you mean something like $H_0: \overline{with lid} = \overline{without lid}$? That's easy for a t-test but I could not tell you, whether there is a symbol for the signed rank sum in Wilcoxon's test. Or maybe I don't understand the question. – Bernhard Sep 28 '16 at 12:54