Multiply Probabilities vs. Sum of the Squares

In summary, when dealing with uncorrelated probabilistic events, if they are independent, you multiply the probabilities. However, if they are correlated, you can use the sum of the squares of the standard deviations to calculate the variance of the sum. It is not common to use the sum of the squares of the probabilities as it can result in a number greater than 1, which is not a valid probability.
  • #1
jaydnul
558
15
Hi! I'm getting confused by these two things. If I have two uncorrelated probabilistic events, and I want to know the probability of seeing them both land beyond 3.3 sigma (for example), do I multiply the probabilities .001*.001 or do I do sum of the squares sqrt(.001^2 + .001^2). I assume it is the former, but can you explain what context we would use sum of the squares instead?
 
Physics news on Phys.org
  • #2
jaydnul said:
If I have two uncorrelated probabilistic events, and I want to know the probability of seeing them both land beyond 3.3 sigma (for example), do I multiply the probabilities .001*.001 or do I do sum of the squares sqrt(.001^2 + .001^2).
Uncorrelated and independent are different things. If they are independent then you multiply the probabilities. Correlation is simply one specific type of dependence. However, it is easy to come up with examples where one event causes the other with 100% certainty (so the probability of seeing them both is equal to the probability of the cause) and yet they are uncorrelated.

jaydnul said:
explain what context we would use sum of the squares instead?
I don't know of a context where you use the sum of the squares of the probabilities. That could easily lead to a number greater than 1, which couldn’t be a probability.

Often you use the sum of the squares of the standard deviations. For example, to calculate the variance of the sum of two random variables.
 
Last edited:
  • Like
Likes PeroK and FactChecker
  • #3
Ok thanks that makes sense!
 

1. What is the difference between multiplying probabilities and sum of the squares?

Multiplying probabilities is a way to calculate the likelihood of two independent events occurring together, while sum of the squares is a mathematical operation used to find the total of squared values. These two concepts are unrelated and serve different purposes.

2. When should I use multiplying probabilities and when should I use sum of the squares?

Multiplying probabilities should be used when calculating the likelihood of two independent events happening together, such as flipping heads on a coin twice in a row. Sum of the squares should be used when finding the total of squared values, such as in statistical analysis or calculating energy in physics.

3. Can multiplying probabilities and sum of the squares be used interchangeably?

No, they cannot be used interchangeably. Multiplying probabilities and sum of the squares serve different purposes and have different calculations. Using one in place of the other can lead to incorrect results.

4. How do I calculate multiplying probabilities and sum of the squares?

To calculate multiplying probabilities, multiply the probabilities of each event happening together. For example, if the probability of flipping heads on a coin is 1/2 and the probability of rolling a 6 on a die is 1/6, the probability of flipping heads and rolling a 6 is (1/2)*(1/6) = 1/12. To calculate sum of the squares, square each value and then add them together. For example, if we have the values 2, 3, and 4, the sum of the squares would be (2^2) + (3^2) + (4^2) = 4 + 9 + 16 = 29.

5. How are multiplying probabilities and sum of the squares used in scientific research?

Multiplying probabilities is used in probability and statistics to calculate the likelihood of multiple events occurring together. This is important in fields such as genetics, where the probability of inheriting certain traits from both parents needs to be calculated. Sum of the squares is used in statistical analysis to find the total of squared values, which is used in various equations and models to understand and analyze data in fields such as physics, economics, and psychology.

Similar threads

  • Set Theory, Logic, Probability, Statistics
Replies
2
Views
1K
  • Set Theory, Logic, Probability, Statistics
2
Replies
57
Views
2K
  • Set Theory, Logic, Probability, Statistics
Replies
1
Views
108
  • Set Theory, Logic, Probability, Statistics
Replies
7
Views
486
  • Set Theory, Logic, Probability, Statistics
Replies
7
Views
342
  • Set Theory, Logic, Probability, Statistics
Replies
2
Views
1K
  • Set Theory, Logic, Probability, Statistics
Replies
12
Views
2K
  • Set Theory, Logic, Probability, Statistics
Replies
2
Views
1K
  • Set Theory, Logic, Probability, Statistics
Replies
18
Views
2K
  • Set Theory, Logic, Probability, Statistics
Replies
5
Views
1K
Back
Top