I'm coming across questions in Biostats which ask to test the hypothesis through χ2 test that $-$
A drug it better than a placebo.
Not that the effect of the drug is not the same as the placebo.
Heterozygotes with sickle cell trait are more resistant to malaria than individuals homozygous for the normal gene. (Q-27 of this book)
Not that the proportion of the individual with sickled cell trait with heavy infection is not the same as the proportion of the normal individual with heavy infection.
What I understand of Chi-square:
The chi square is a measure (square) of deviation of an observed sample from a standard data/proportion/frequency, it does not indicate the direction of the deviation (i.e. it is not positive,negative and zero as z-score but is only positive and zero). If the data is a good fit with theoretical, the χ2 would be less or in fact zero (something out of shear chance) and the value will increase with deviation.
So, should (is) χ2 test be used to determine the direction of deviation?