Jo wrote in news:[EMAIL PROTECTED]: > "Dirk Van de moortel" <[EMAIL PROTECTED]> > wrote in message news:[EMAIL PROTECTED] >> >> from which you can easily algebrate and calculate mu1 and mu2 ;-) > > Thanks for the answer. I've worked out how to do most of it, and I > have an equation to use. > > The equation is CL (lower) = xbar - z(st.dev/sample size) > > It have applied it fine in case where z has been supplied. What I need > to know though is how do I get the value of z? 'z' is defined as "the > (Normal) value such that P(-z < Z < z) = CL. > > I have no clue how to get it - I tried to get it via the Inverse > General Normal table but I couldn't match the value that was supplied > to me. > > e.g. Confidence Level 0.90 then z = 1.645 > The usual method: You go to a table of the CDF of normal distribution, N(0,1). (I think the CDF is generally easier to find than the Inverse table.) It is generally laid out with values of x and Phi(x) and centered on 0 so Phi(0)=0.500 . Phi(x) is the Normal CDF. You find the value of x that gives you the needed value of Phi(x), in your case 0.95, since you want centered 90% limits. The value of x that does that is 1.645
It should be possible to do it with the Inverse table, though. Phi^-1(1.645) should equal 0.95 -- David Winsemius . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
