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I'd like to replicate this. I propose a very simple experiment: 

Every Monday and Wednesday, for 5 weeks, I will send 10 people across the US a single postcard selected at random from three types: Christian, Atheist, and neutral.

The recipients will report the date stamped on the card, the date of receipt, and the type of card received. 100 in each of 3 categories should be enough to detect any variation.

1. If you'd be willing to be a recipient and are in the continental US, please contact me privately with your mailing address. Please note that you MUST check your mail every day for about two months — I want to be sure that I get accurate delivery times.

2. I could use a delivery of postcards to use. They should be 100 extremely Christian, 100 extremely Atheist, and 100 total bland nature photography. If you can provide this, please contact me privately.
Qítiān Dàshèng Sūn Wùkōng (Andrew Dalgleish)'s profile photoMark Hall's profile photoNoel Yap's profile photoSai (saizai)'s profile photo
I think it would be interesting to toss in Muslim, FSM, Hindu and Jewish as well. Is it atheism, or recognizable non-mainstream?
I think an additional interesting data point would be to add in something larger and more concealed, maybe like those bubble-wrap paper envelopes small electronics get sent in.  My first thought being maybe there's an arbitrary part regarding what mail gets extra scanning, swabbing, etc, thus maybe the people selecting mail to route to scanning have extra suspicions about atheist labels.  So running it with postcards and also packages would help us see if there's a difference between postcards which can be eyeballed and packages which might call for scanning.  Then compare that against the thing you linked which has the additional factor of international origin.  Maybe ask THEM to do a set of postcards as well if you get interesting results between postcards and packages.
Ooh ooh ooh!  When you do your copcards, have an option to join in the test group, where you pay a bit more to get your copcards shipped in the bubble envelope, agree to check your mail every day for n period of time, and then also get in the postcard group.  Seems a reasonable possibility people who would order copcards might also be willing to contribute to this study, so bundle them.  Also maybe offer an option to pay more but not participate (cuz don't wanna check mail every day - that's why I'm not signing up - etc), instead funding someone else's participation.
I wasn't sure how to contact you privately, so I put my address in a post shared with a circle containing only you.  Hope it works.  Add a comment to that post, please, if you get and decide to use the address.
+Mark Hall , FYI, you didn't need to create a one-person circle. You could've just +'ed him in a separate post.
+Sai , one of my friends brought up the fact that postcards are handled by machines for the most part.
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