Why not just testing alternative hypothesis? Why do we need null hypothesis? Why not just testing alternative hypothesis? Why do we need null hypothesis?
For example, I am testing the effectiveness of a new drug. I can choose two groups: control and experimental. Based on the result I can say that whether the drug is working or not. Why do I need to state the null hypothesis in this case anyway?

because alternative hypothesis (Ha) will have a certain degree of correlation attached to variables, like strongly correlated or weakly correlated. Suppose you simply state Ha, then ppl will ask how strong is the correlation between variables. Suppose its weak correlation, again ppl will question, how much weaker? suppose Ha is very weak almost close to Zero, in such cases you'll need Null hypothesis (Ho) to make a distinction between Ha and Ho
