What should we consider the null hypothesis?
A test statistic is a statistic used to measure the plausibility of an alternative hypothesis relative to a null hypothesis. (The statistical Sleuth)
From this it can be concluded that the alternate hypothesis should be the scientific hypothesis one is trying to establish.
Now this is from a blog I'm using to understand stats
The null hypothesis, H0 is the commonly accepted fact; it is the opposite of the alternate hypothesis. Researchers work to reject, nullify or disprove the null hypothesis. Researchers come up with an alternate hypothesis, one that they think explains a phenomenon, and then work to reject the null hypothesis.
Even at my college this was taught.
But recently I have started taking help from a Stats teacher who along with a Zoology Practical book by P.K. Banerjee is of the opinion that our scientific hypothesis should be the null!
Infact I came to know that when we are not sure what we should be deducing from our data we test if it is consistent with any known theoretical data. It is then that null becomes central,i.e. the hypothesis the scientist is interested in. I found this also in wiki example.
Is this what makes the two types of assumptions different?
Discussing with a problem
A professor wants to determine whether her department should continue keeping the prerequisite for an introductory stats course that the students applying must [preferably] have college level algebra in previous curriculum. She decided to find out from an year's result of that course.
With algebra = 34 (passed) & 6 (failed)
Without algebra = 12 (passed) & 18 (failed)
Are students who had college level algebra in their previous curriculum were more likely to pass the course?
[A chi square contingency]
Ho= The students who had college level algebra in their previous curriculum did not have a greater likelihood to pass the course over those without algebra.
Ha= They did have.
The calculated Chi-square was smaller than critical value and so the null was accepted.
Now the Stats teacher said that it would be the opposite.