10
Currently, it is a timer which counts down from 10 minutes starting when the transaction is first seen. When the timer reaches 0 minutes, it switches to "Unknown / Never."
It is my understanding that finding blocks (and confirming transactions) is a Poisson process, hence the correct value should be a constant "10 minutes" and then "Confirmed!"
Is my understanding wrong?
7
You're correct; the expected confirmation time from any given point in time is always around 10 minutes (it may be a little more or less when the network hash rate has changed since the last difficulty adjustment). This question looked at that exact issue.
Note that a retailer (or other transaction acceptor) doesn't necessarily need to wait for a block to be solved in order to accept a payment though. More info here:
2
The expected confirmation time should really take the priority of the transaction into account. If a transaction has insufficient fees attached to it then it will tend to take longer to confirm.
I don't know if blockchain.info takes this into account or not.
0
I don't think you understand what a Poisson process means. It does NOT mean that there is a constant time interval in between events. It means that it is a random process in which events are independent of each other. There is an average time interval, but this is by no means constant and it is NOT even the same as the "expected" time interval. The bitcoin difficulty is designed to have an average interval between blocks of about 10 minutes. I have made a table below, showing what this means if you take Poissonian statistics into account. It shows the percentage of transactions are are expected to complete within the specified number of minutes. Some interesting insights are that about 1/3 of all transactions are confirmed in less than 4 minutes. The converse of this is that in 1-2% of all cases, it takes up to 40 to 50 minutes for the first confirmation to occur. The way to rationalize this is simply to understand that the process is random--so some intervals will be longer than others. And since it is possible for some confirmations to take place very soon after each other, then obviously some confirmations will be very far apart in order to "justify" the average interval between confirmations.
Minutes % Confirmed
0.5 5%
1 10%
2 18%
3 26%
4 33%
5 39%
6 45%
7 50%
8 55%
9 59%
10 63%
15 78%
20 86%
25 92%
30 95%
40 98%
50 99%
You're exactly right, but the expectation value for time to next block is always 10 minutes (assuming difficulty and network hashrate are equilibrated). As you said, finding the block is random, so 8 minutes after the block N, the mean time to block N+1 is 10minutes. – Streblo – 2013-07-04T06:40:22.970
I think the OP does understand what a Poisson process is, but the authors of blockchain.info don't. – Nate Eldredge – 2013-07-05T01:27:44.873
Ok. thanks guys. Now that I re-read the OP's question, I see that I was misinterpreting it. It's true that at any point in time, the expected time until the next block is 10 minutes. – drwatsoncode – 2013-07-30T15:00:01.517
It doesn't appear as so. This is what I originally hoped for when I saw this (unfortunately lackluster) feature. – Streblo – 2012-07-09T06:31:58.670
+1 Good point, Chris. To provide an accurate estimate though, you'd have to research the relationship between transaction fee and confirmation time. I suspect a transaction with any fee at all would be included by most miners while the block reward is high, but that's likely to change in a few years time as the reward drops. – Highly Irregular – 2012-07-09T08:07:14.540
1Other factors come into play - some miners seem to be deliberately avoiding transactions to and from SatoshiDice addresses for instance. Also the relationship between the size of the fee, the size of the transaction, and the ages and sizes of the inputs of the transaction needs to be taken into account. – Chris Moore – 2012-07-09T10:38:38.540