主题：葫芦僧乱判葫芦案 -- 煮酒正熟

Why do you say our two groups are not from the same universe? I already explained several times, it's not the 3000 card users against the other 3000. It's the 5000 (among which there're 3000 card users) against the other 3000. Please tell me why they're not from the same "整体"?

As for assumptions validation, I believe you can do either way. You could first check the assumptions before running the test, or you could first run the test and then check for assumptions. In the first approach, if the assumptions do not hold, you need to recreate your testing samples, while in the second approach, if the assumptions do not hold, the quality / accuracy of your conclusion is at risk. It all depends on how serious those assumptions are violated, and which assumption is violated. (Normally the equal variance is more critical than normality.)

I don't know exactly how our statisticians are handling above problems, but I'm pretty sure they will exercise their professionalism in due course. How do you know they didn't do their job well? My original article didn't say our statisticians already checked for those assumptions, but this by no means should be interpretated as they did not check.

Finally, that VP does not know the first thing about statistics. So by pointing out any errors related to statistical analysis in our job does not prove or support the correctness / appropriateness of his decision of not accepting our proposal. If the VP were a statistician, then your challenge on our statistical analysis would make more sense.