Topic: Fair and unbiased coins have a bias to land on the same side they started (Read 314 times)

Perhaps the subjects shouldn't have known what the purpose of the test was. But they began the experiment knowing what they are trying to prove. The writers of the research paper mentioned that concern as well, and I agree with them.  

I think the 3749201 PIN is more secure than 0011110 simply because it uses a greater variety of digits. In the first PIN, you only have zero's and one's. In the second one, you have seven different numbers. My layman's conclusion is that the first PIN would be easier to bruteforce than the second one. 

I also wonder the same.  In theory the more you flip the closer to 50 percent you will get.  This is very reminding of Gambling where you think 50 percent chance of win means out of 10 rolls you will win 5 and lose 5.  But it is very possible to win 10 in a row just as much as none.

What if after all these 300+ thousand flips they try 10 thousand times more and 9 out of 10 thousand flips the opposite side lands only.  It changes the outcome.  Now the 10 thousand flips had 90 percent bias.

Interesting nonetheless.  Statistics are EXTREMELY annoying to me.  I would say, why not ask the 48 people at the end whether they thought about manipulating the results.  But then what if some of them lie.  What if all of them lie!  Then why not blindfold them, put a coin inside a cone, hand them the cone and let them throw.  But how random is the movement of their hands really?  What if the way some body throws a coin marks the actual landing.  UGH!

I have no idea!  How do you measure security of random?  We are humans after all and even if we TRY flipping a coin 100 times the same way we will not do it the EXACT same every time.  So there is some sort of random in that.  Even if you try to manipulate.

A manipulator could fail at manipulating the toss.  What if the manipulators actually landed more randomly than the rest.  How do you measure?!

My mind says DON'T TRUST HUMANS AT RANDOM GENERATION but how random is random really.  I had a few happenings where I generated a random number of 5 to 10 digits and it generated me a number like 0011110.  It was maybe random.  But putting this into Security, how secure is the PIN 0011110 compared to the PIN 3749201?  How random was the PIN I just 'randomly' pressed on my keyboard though?  Does it make my PIN less secure than the 0011110 randomly generated PIN?

The more I think of this the more my brain goes, WHAT THE FUCK!  The more you get to a perfect statistic the better you realize there is no such thing.  Closest you can get is a 'more perfect' statistic.  But is it really?

It's worth pointing out that this test had 48 participants who participated in the coin tossing. It wasn't only one person. They all had varying degrees of bias for the same side, and about a dozen of them showed a bias to the opposite site. The 51% chance that the coin will land on the same side is an average taken from all participants and all tosses.

hmm if he did the exact test again and got 51-49 again it is a lot more likely there is a bias.

This is exactly what I hoped I wouldn't get as an answer 

Do you think this "thesis" proves anything? To me it doesn't!

Probably because someone getting a degree in statistics had to choose a subject for their thesis and odds are this was easiest...

This is interesting.

I will read the paper, but I don't have enough time currently.  To be honest I am not surprised. However, can someone who has read the paper tell me why did the choose to do this research? I mean we all know from our school years that true coin toss will give 50% as long as the number flips tends to infinity.

So couldn't it be just a coincidence even though the flips where that many?

There are videos of the coin toss experiments but I haven't watched any of them. I don't think they tossed the coins over their heads to land behind them, but if you are interested to check it, you can find the videos at https://osf.io/mfkp9/. Each video has to be downloaded. It seems the site doesn't support video streaming in-browser.

Didn't they just prove the exact opposite?
Theoretically an unbiased scenario would be if the coin had a 50% chance of landing on the same side. They proved there is 51% chance for that. Correct me if I'm wrong but I wouldn't call 1% in a rather small batch with a lot of other variables to be the bias. It looks more like the negligible error (ie. 50% ± 1%).

It is not worth it since at the end of the study your thumb would stop working

Good way to say it.  The key is lots of rotation of the coin. Although a very disciplined and skilled athlete may be able to play with that.

But I suppose it is like bowling a bowling ball on a 300 foot alley vs a 60 foot alley.

Lots of people have a perfect game on a 60 foot ally. I would suspect no-one would be able to do it on a 300 foot alley.

In the interest of being thorough, it should be pointed out that most washers *will* have a built-in bias because most have a rounded top edge and a much sharper bottom edge because they are stamped out of ribbons of metal. For no bias the washer should be flat-ground.

As an aside - that also affects how they work: correct orientation is rounded side against the head of a bolt or against a nut or lock-washer, sharp edge against what is being bolted. The edge digs in to grip the material a bit reducing chance of rotation and also helps seal against corrosion.

As for bias caused by how a coin is flipped - take that out of the equation by spinning it on the edge and counting what side it stops on. The huge number of spins that usually happen should remove any conscious or unconscious 'flip' technique bias.

But did they be sure to make the coin spin and that it must go upwards over the head of the tosser.

I can favor a half dollar or a silver dollar if I flip it to a soft surface such as grass. And I start it on heads or tails I can bias the toss by doing a gentle lower toss.

say my hand releases at waist high and it arcs up to chest high and fall to grass with a slower spin.

Much like tossing a dart at a bulls eye  you can do some control over the coins.

But If you have to make the coin toss go over your head and spin rapidly hitting a hard surface like a maple wood floor control is far more difficult.

The bias is very likely subconsciously done by the tosser.

If you tested this with blindfolding I wonder if it changes.

I know, but they mention that comparison for the readers to understand how big of an advantage such a side-biased coin toss gives you (on average) compared to some well-known casino games like blackjack and roulette. It didn't have to be in the report. I think saying that you could potentially profit $19 on average after 100 coin tosses if you know the starting position of each coin before it's tossed is enough.

At a quick look they were all coins. I was just wondering if you picked some other thing that you could flip like a coin but was not a coin it would be a different result.

In the end it probably does not matter, just more of a though of how things that should not matter or we think would not matter actually do.
Like flipping a poker chip or washer vs. a coin. But for some reason using those things do change the outcome.

-Dave

Coin toss has nothing to do with casino's house edge and odds, because they are using computer entropy to generate the random numbers that in turn determine the results. It's not affected by any gravitational bias - although some people do point out that heat conditions around the CPU's random number generator(s) might have a slight impact - but that can be mitigated by also using a software RNG like OpenSSL's.

It depends on which casino games you play. The report makes a comparison between the advantages you get with side-biased coin tosses versus the advantage the house has in roulette and blackjack. The advantage and house edge is greater for roulette where the casino would profit more long-term. But blackjack is known as the casino game with the lowest house edge.

They mention that a comparable bet would earn the casino $5 for blackjack, but for single-zero roulette that profit would increase to $27. As mentioned earlier, side-biased coins can potentially earn you $17. 

lets pretend it is true.

how bout alternative spin starts.

A)  you must use heads on top to start flips for first ten tosses
B) you must use tails on top to start flips for second 10 tosses

so on and so forth pretty much ends that issue.  if that issue is true.

Other things need be done when you flip it it must go up and over your head as it is spinning. It must spin.

I would be willing to bet that if done with the same coins as the first test for 350,000 spins it would be more accurate.

Would be interesting to see how something different then coins would behave. i.e. casino chips or metal washers where people are not used to 'heads or tails'

Actually washers would probably be better since they do have a hole in the middle, would that have any factor in it.

-Dave

Wow. I can't imagine the boredom. Must be killing.

It is extremely small. It has been demonstrated in this post and in here, that this particular difference results in a loss of 0.05 bits of entropy when tossed 256 times; even extremely biased dice can provide more than enough entropy if you toss them enough times.

We discussed this paper already in another thread here: https://bitcointalksearch.org/topic/m.62997786

And as I said in that thread, I think a far more accurate take away from that paper is that everyone has their own intrinsic bias. 10 of the 48 participants showed a bias to the opposite side, not the same side, and there was one individual who showed an extreme 60/40 bias.

This remains the gold standard, and simply start each flip from the same starting conditions (i.e. heads up) to completely eliminate any bias in your flipping technique.