When you are using JMP to do a two-sample hypothesis test or confidence interval, watch which way it is subtracting.  It may not do it the way you expected.  For example, you may have called "A" sample 1 and "B" sample 2, so you would expect to do A - B, but JMP may do B - A.  It is difficult to get JMP to subtract a specific way, so it is better to let JMP do what it wants to, and you adjust to it.  Look at the two sample means JMP computes for A and B, then check if the "difference" in its t test values has computed A -  B or B - A.  If it has done B - A, then define your means accordingly.  Which is to say, let μ₁ = mean of B and μ₂ = mean of A, then state your hypotheses accordingly.

 

If you do not do this, your signs will be all wrong.  For example, the signs in your lower and upper limits for your confidence interval for the difference between the means would be the opposite of what they should be.

 

Tip:  If you want to do a one-sided test, if JMP has a positive test statistic, you must be doing an upper-tailed test; if JMP has a negative test statistic, you must be doing a lower-tailed test.  But, again, watch the way JMP has subtracted the two means to identify who is who.