Do paper coupons work better for E-commerce?

I’m curious if anyone has simultaneously experimented with both forms of coupons i.e. sent a paper coupon to a random set of customers, and sent an e-coupon of the same value to another random set of customers. Which set had a higher conversion assuming all other customer attributes of the campaign were similar?

Behaviorally speaking, it’s difficult for most of us to throw out a piece of paper that has the words “Rs. 300 off” printed by a brand that we trust for shopping. It’s like throwing away cash, and we’re wired not to do so. In fact, people love the idea of maximizing “free”.

Google Adwords did a promotion where they gave Rs. 1500 worth of ad-credit. The coupon arrived at my home by postal mail, and I found it hard to throw it out even though it meant I had to open one more Adwords account to use it. I finally did use it on the last day of the offer.

I got similar e-coupons from Cleartrip.com and FirstCry.com, both I can definitely use, but they’ve got buried in my e-mail somewhere. When they arrived I was too busy to shop, and later they’re ‘out of sight’ hence ‘out of mind’.

With a paper coupon, I often bump into it around the house until I physically take the step of throwing it out. That way, at least customers like me who intend to use the coupon are reminded automatically without the company having to spam everyone who did not use it.

“Going green” implies that companies should avoid paper and send e-coupons, but I’m curious if paper converts better for brands that send coupons only occasionally. One uses the unlimited storage of your inbox, whereas the other uses the limited space on your dining table or bookshelf.

This is just my hypothesis. Do share any data or behavioral anecdotes. I would love to get a conclusive answer.