What is the difference of "PROC SORT NODUP " and "PROC SORT NODUPKEY"?
NODUP will delete the observations which are exactly the same in all variables. NODUPKEY will delete the observations which are identical in the "BY" variable(s).
When we want to know a maximum value of a curve, y = 5+ x^2 (x square), what is the solution by using derivative?
Find the derivative of y = 5+ x^2 , which is 2*x, and when this equals to 0, we have the max value of y
When we are using t-test to compare the mean of two groups, for example, we want to find out, whether there is a significant difference in the height of two groups of girls. What assumption we need before we are using t-test?
The mean of the height of two groups is asymptoticly normally distributed.