All Questions
Tagged with sum standard-deviation
8
questions
1
vote
0
answers
24
views
Summing multiple standard deviations (repeated measures) [duplicate]
Say a set of 5 participants completed two subtests (A and B). The scores on these subtests can be summed to get a total test score. Here is the dummy data:
Participant
Subtest A
Subtest B
Total test
...
- 31
1
vote
1
answer
45
views
Sum of estimated costs for uncertain events
I have a number of possible events $e$ with a probability $p_e$ of the event occuring and a cost estimate should the event occur (if it doesn't occur the cost is 0). The probability for each event is ...
- 13
1
vote
0
answers
39
views
property about the standard deviation of 2 r.v.
If $X,Y$ are $\geq 0$ random variables, how to demonstrate that: $$2*Stdev(X) \leq Stdev(X+Y)+ Stdev(X-Y) $$
$Stdev$ represents the usual standard deviation.
- 41
2
votes
0
answers
1k
views
How to calculate a new mean from different means for my Systematic Review and how to calculate a new SD?
I am currently doing a systematic review on distal radius fractures. I want to give a mean age and sd in my systematic review. Therefor I need to calculate the mean from all the different means of the ...
- 21
5
votes
1
answer
1k
views
Measuring share contribution of each var/cov term to the standard deviation of a sum of variables
Say, for a simple example, I have a random variable $X = \alpha_1 X_1 + \alpha_2 X_2$, where $X_i$ are random variables and $\alpha_i$ are weights. I then calculate the standard deviation of $X$ as $\...
- 151
2
votes
0
answers
40
views
Standard deviation of number of terms in a sum
If some random variables are drawn from a normal distribution N(m, s) with m > 0 until the sum of the draws exceeds some ...
2
votes
0
answers
612
views
Summation of a product
I need to calculate the following expression:
$$\sum_{k=1}^N a_k b_k$$
${a_k}$ and $b_k$ are real positive numbers. N and k are integers.
I know the average values of $a_k$ , defined as $\overline {...
- 21
1
vote
1
answer
229
views
Estimate variance of sub-sets from overall variance
I am looking for a way to estimate the variance of a summed sub-set based on the variance of those sums.
Si = sum( Ai )
S = { S0...Sn }
V = variance( S )
That is,...
