Wikipedia:Reference desk/Archives/Mathematics/2008 September 19

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September 19[edit]


what is the probability of 1.0 means? and between probability of 1.0 and o.4 which the best to present the survival without parasitemia —Preceding unsigned comment added by (talk) 07:53, 19 September 2008 (UTC)

A probability of 1 means that it is certain (100% likely) to occur. A probability of 0 means it is certain to never occur, 0.5 means the event will happen half (50%) of the time. A probability cannot be less than 0 nor can it be greater than 1. -- SGBailey (talk) 07:58, 19 September 2008 (UTC)
This is wrong. If an event has probability 1, it does not mean that it is certain. For example, consider the event of randomly picking a number in [0,1]. The probability that you pick a number other than 0 is 1 but it is not certain that you will not pick a 0.

See Almost surely.

Topology Expert (talk) 05:44, 20 September 2020 (UTC)

Please clarify your second question. Are you asking whether 1 or 0.4 is a more reasonable measure of a survival rate without parasitemia? Note that survival rates are usually associated with a certain length of time. Zain Ebrahim (talk) 14:15, 19 September 2008 (UTC)

Though maybe it should be noted, from a mathematical and not at all practical stand point, that probability 1 is not quite certain and probability 0 is not quite "certainly not". Thenub314 (talk) 14:57, 19 September 2008 (UTC)

Eh? From a mathematical point of view, 1 is certain and 0 is certainly not. From a colloquial point of view then anything goes. Use "Acme's gadget for 110% success" is gibberish mathematically. -- SGBailey (talk) 15:16, 19 September 2008 (UTC)
1 is not certain; see my previous comment.

Topology Expert (talk) 05:47, 20 September 2008 (UTC)

What Thenub314 means is that any set with measure zero has probability zero, not just the empty set. Pick a random real number between 0 and 1. The probability of your picking that number was 0, yet you picked it. -- BenRG (talk) 16:28, 19 September 2008 (UTC)
We have an article: almost surely. Algebraist 16:31, 19 September 2008 (UTC)
Note that there is a subtle difference here between the theory and practice in that we have no way to pick a random real number between 0 and 1. So when you pick a random real number, it actually has some nonzero probably. Even with a true random number generator, there is only a finite list of expressible numbers.
To my knowledge, everything in practice is a finite process, and so there is no practical distinction between almost surely, and certain: and the OP probably doesn’t know any measure theory. GromXXVII (talk) 13:30, 21 September 2008 (UTC)