主题：葫芦僧乱判葫芦案 -- 煮酒正熟

In theory, what you've suggested is fine. But in reality, it's just not correct.

By turning down those 1,500 best customers of their right to use PLCC, you'll piss them off and hurt their loyalty to your brand. A certain percentage of these customers would switch to your competing brands and that's the least thing that you wanna see.

Secondly, from a pure theoretical stand point, the very act of denying the cards to those 1,500 people actually changes the quality of these people. To be more specific, this will hurt their loyalty, emotional attachment, and the passion associated with your brand, hence turn them to a lower quality group. In other words this group is no longer the group before! And you're still using them as the control group?? In this case you would over-estimate the impact of the card.

So the only theoretically correct and practically viable and appropriate approach is, you first randomly pick 5,000, propose the card to them, and let them decide at their free will. Then you'll have two groups of customers, the first group, say, 3000 people, being those who choose to use the card, and the second group (2,000) who choose not to use the card. These 3000 plus 2000 would be your Test Group.

Then you pick another 3000 people who belong to the same decile but are mutually exclusive from those 5000. This will be your control group.

Then you evaluate the performance of the whole Test Group (not only those 3000 card users) and the Control Group, do the comparisons and then draw a conclusion. This is exactly what we're doing right now, and the difference is more than 26%.

I don't see any flaws here. Can you?