Does Sharing Contest Invitations on Facebook Increase Your Chances of Winning? Do the Math.

“Jean Georges Dinner”, reads the message title in my in-box. That’s enough to get my attention, spam or no. I open the email. It’s a contest at Bloomspot for a seasonal wine tasting and pairing for two at Jean Georges.

That’s a no-brainer. I click the link embedded in the email, fill in my email, zip code and city, and click Enter. Jean Georges here I come! Wait, what’s this?…

Increase your chances. INVITE FRIENDS.
Get a bonus sweepstakes entry for each friend who enters.

Hmmm… “Increase your chances” Chances of what? I notice they did not say “increase your chances OF WINNING”.

Now I’m not dumb. I know that increasing the contestant pool is not a good thing when it comes to improving one’s odds of winning a contest.

But they are giving me additional contest entries. Doesn’t each additional entry effectively double the odds in my favor? Hmmm…This may not be as simple as it looks.

Time to do some math.

(I know, I know…I have much better things I should be doing with my time. But I just saw Moneyball, and am re-enamored with statistics. And you know me, ADD-girl,  I just head where my brain takes me… )

It’s interesting when you do the numbers. Those extra contest entries you get for sharing on Facebook initially do increase your absolute odds of winning. But those odds only stay increased if the pool of contestants doesn’t grow or move more than a level or two beyond the initial share. Because once it does, the whole thing actually starts to work against you and everyone else, and your absolute odds of winning become really, really low. At which point, having more shares actually increases your relative odds of winning over having less shares.

Let me show you…

• Suppose I am the 100th entrant into the contest. My chances of winning are 1/100 or 0.01.  I send you a Facebook invite, and you enter. Now my chances are 2/102 or 0.0196. Hey, it worked! I increased my chances!
• So I send an invite to a second friend, who also enters. Now my chances are 3/104 or 0.028. Whoo-hoo! Sharing is power! But wait –
• What if my first and second friend each invite two friends? This dilutes my odds, but actually not by much.  My chances are now 3/112 or .0267.  I’m still ahead.
• But what if 10 friends accept the invitation, and each friend has another 10 friends who accept it, and each of those has 10 friends who accept it?  Then my odds become 11/2320 or .004 – lower than they were when I first entered the contest!
• On the other hand, my friends and I are not the only ones in this contest. Suppose, when all is said and done, the contest has 50,000 entries, including me and my pool of friends and our 2219 entries (excluding the initial 99 entries before I joined).
• My odds with sharing would be 11 in 50,000 or .00022.
• My odds without sharing would be 1 in 47,781 or .00002. So sharing increased my odds by tenfold – but just  look how low all of our odds have become!
• What if I and the first 100 entrants decided not to share with anyone else on Facebook? We’d all have much better odds than we’d ever have by sharing. But talk about trying to get the cat back into the bag…

Bottom Line

Sharing contest invitations on Facebook is fun, but the more everyone shares, the lower the odds of winning for everyone. (So stop sharing everyone, will you?…) Once a contest gets big, sharing can increase your minuscule odds of winning to slightly less minuscule, so you might as well go for the big share and enjoy the ride. Understand you are sharing your email address, effectively building up a mailing list for the contest sponsor, which was probably the whole point of the contest in the first place.

If you really want to win something, stick to your church raffle. The odds are much better.

And if you want to keep your odds up in a contest, definitely do not blog about it, since now you’ve told everyone, and you didn’t even get a single extra sweepstakes entry.