My understanding of null and alternate hypotheses :
The null hypothesis is a hypothesis whose plausibility is being tested by a test statstic and is denoted by H0. It assumes that observed data follows a standard scientific theory (and the variation/deviation is due to chance).1 Alternative hypothesis is a hypothesis that contradicts null hypothesis. It assumes that the variation in the observed data is real, not due to chance.It is usually the hypothesis that a scientist is trying to establish. (Source: Biostatistics by Lee & Forthofer & Statistics by David Freedman)
This1 holds good for Goodness-of-fit test but not chi-square test for independence as there is no theoretical data to compare the observed data with.
So my question is in a given problem of chi-square test for independence how to determine what the null should be?
When what the scientist is trying to establish is mentioned:
Q : In a study of effectiveness of an antipsychotic drug, patients are treated with the drug and were compared to those receiving a placebo. 698 of 1068 patients were released after taking the placebo while 639 out of 2,127 relapsed after taking the antipsychotic drug. Test the prediction that the antipsychotic drug is significantly more effective in preventing relapse than placebo.
A: Ho : Edrug = Eplacebo Ha : Edrug > Eplacebo
(Reasoning: Ha is the hypothesis the scientist is trying to establish and so Ho should be something that opposes the Ha that he has to disprove.)
When what the scientist is trying to establish is not mentioned (at least not clearly):
Q: Among 60 males and 50 females, 25 males and 20 females were with attached ear lobes. Statistically prove whether or not the attached pinna has any relation with sex.
Not sure what the scientist wants to establish so unable to assume a null.