I have a design that gives me the following (150*12*4)/6 = 1,200 which IS greater than the more conservative 1,000 rule of thumb. However, when I run an advanced simulation, my biggest attribute which has 6 levels is giving me standard errors in the .06 range...which is higher than that test's <.05 rule of thumb. I would guess the simulation is more robust but .06 is not that much higher than .05. I would need my sample size to be closer to 215 to get my errors to .05 or below.
Curious about the perspective here? Is it critical that we get the sample up to 215 (or higher) or a nice to have or somewhere in between? Realizing that more is always better, from a practical standpoint, am wondering how much to push the add'l costs and my client to move it up - its always a matter of degree.