What is the probability of two independent events occurring simultaneously?

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Discussion Overview

The discussion centers on the probability of two independent events occurring simultaneously, particularly in the context of probability density functions (PDFs) for continuous and discrete distributions. Participants explore the implications of independence and the nature of the distributions involved.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the probability of two independent events occurring simultaneously can be found by multiplying the results of their respective integrals over time.
  • Another participant counters that for continuous distributions, the probability of two independent events occurring at the same time is 0.
  • A different participant inquires about calculating the probability of two events occurring between specific time points 'a' and 'b', using examples of light colors.
  • One participant asserts that if the events are independent, the probabilities can be multiplied, but if they are dependent, a joint distribution must be known.
  • Another participant challenges the claim that continuous distributions cannot yield non-zero probabilities for simultaneous occurrences, providing an example involving independent normally distributed random variables.
  • A later reply clarifies that the original question pertains to the probability of exact equality between two continuous random variables.

Areas of Agreement / Disagreement

Participants express disagreement regarding the treatment of continuous distributions and the probability of simultaneous occurrences, with multiple competing views presented without a clear consensus.

Contextual Notes

The discussion highlights the complexity of defining simultaneous occurrences in the context of continuous versus discrete distributions, as well as the need for clarity on independence and dependence in probability calculations.

oneamp
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Hello. I have two probability density functions for two events. I would like to find the probability that they both will occur at the same time. It is simply multiplying the results of the two integrals over the time, correct?

Thank you
 
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oneamp said:
Hello. I have two probability density functions for two events. I would like to find the probability that they both will occur at the same time. It is simply multiplying the results of the two integrals over the time, correct?

Thank you

No. Two events can occur at the same time only if they have discrete distributions. When both have continuous distributions (and are independent) the probability of happening at the same time is 0.
 
Yes true :) How can I calculate the probability that between some points 'a' and 'b' in time, two events with these PDFs will occur? For example, if one PDF describes the probability that a light will be orange, and another PDF describes probability for a green light, and I want to know the chances that there will be an orange and a green light illuminated "at the same time" between times 'a' and 'b'?
 
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oneamp, if the two events are independent then you can simply multiply the probabilities of each even happening. If they have some dependence between each other then you need to know exactly what that dependence is - you have to have a pdf p(x,y) which is called the joint distribution between the two variables.
 
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Thank you very much
 
mathman said:
No. Two events can occur at the same time only if they have discrete distributions. When both have continuous distributions (and are independent) the probability of happening at the same time is 0.
That's not true at all. Suppose ##X## and ##Y## are independent normally distributed random variables. Let ##A## be the event that ##X > 0## and ##B## be the event that ##Y > 0##. Clearly the probability of ##A \cap B## is nonzero.
 
jbunniii said:
That's not true at all. Suppose ##X## and ##Y## are independent normally distributed random variables. Let ##A## be the event that ##X > 0## and ##B## be the event that ##Y > 0##. Clearly the probability of ##A \cap B## is nonzero.

You misunderstood the point of the original question. He was asking about something like the probability that X=Y when both have continuous distributions.
 

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