All Questions
14
questions
4
votes
2
answers
121
views
Confidence interval for the sum of 2 binomially distributed variables
$P_1$ and $P_2$ are uncorrelated, binomially distributed variables with success probabilities $p_1 \neq p_2$. Say I measure:
$k_1 = 9$ successes out of $n_1 = 10$ trials for $P_1$ and
$k_2 = 1000$ ...
- 41
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
0
votes
0
answers
77
views
Average of random variables from two Poisson distributions?
I'm lost with a very simple question of finding the average of random variables from two Poisson distributions. I know that if $X\backsim Pois(L1)$ and $Y\backsim Pois(L2)$, then $X+Y\backsim Pois(L1+...
- 145
3
votes
0
answers
102
views
Mean number of throws to exceed a threshold [duplicate]
Say that you have a die with n faces, and you need to throw the die until the sum of your results exceeds a given threshold.
What is the average number of throws needed?
I think that to compute that ...
- 181
2
votes
1
answer
588
views
Proportion of the sums or average proportion of the parts?
Here’s a curiosity that come up during a work discussion. While this example uses financial data, it has a statistical question at its heart.
Consider the following table with a budget and actual ...
- 890
4
votes
3
answers
2k
views
What does "The mean of the sum of N independent variables with the same distribution is N times the mean of a single variable" mean?
I have been reading a book about statistics for physicists and there was this line given: "The mean of the sum of N independent variables with the same distribution is N times the mean of a single ...
- 143
1
vote
1
answer
212
views
Why is $\sum{(x_i-\overline{x})^2}$ = $\sum{(x_i-\overline{x})x_i}$ true? [duplicate]
I have seen this equality many times in books but I never found an explanatory derivation.
- 117
0
votes
1
answer
117
views
Summation of two Gaussian distributed data with different coefficient of mean and variance
I need some help on Gaussian distribution. i have two dataset, both are identical and independent distributed, but having mean as 2μ_1 and μ_2, same scenario for the variance. How can I add them?
...
0
votes
2
answers
720
views
Summation of squared x_i if summation of x_i is 1
How to prove "If $\sum_{i=1}^n x_i=1$, then $\sum_{i=1}^n x_i^2>1/n$"?
I'm thinking about $Var(x_i)=E(x_i^2)-[E(x_i)]^2=\frac{1}{n}\sum_{i=1}^n x_i^2-1/n^2\ge0$. Is that correct?
- 3
5
votes
1
answer
4k
views
Distribution of the sample mean of Poisson random variables
Suppose that you have data x which is modeled as a realization of a Poisson random variable X with expected value $\lambda$>0. I know that the sum of Poisson random variables is also Poisson ...
- 53
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
0
votes
1
answer
22k
views
In SPSS, should I calculate the mean score or the total sum score?
Are there any differences between mean scores and total sum scores? I know how to calculate both, I just don't know if there is one of them that is preferable?
Also, the scores will be used for t-...
- 11
4
votes
1
answer
183
views
Sum of products in an expected value
A box contains $n$ balls numbered from 1 to $n$. Suppose you take a ball at a time, putting it back on the box, until you pick a ball twice. How many balls are you expected to take from the box?
Let $...
- 425
0
votes
1
answer
11k
views
Sum(XY) in terms of Xbar and Ybar [closed]
If $x$ and $y$ are two series, is there any relation between $\sum{(x,y)}$ that can be expressed in terms of mean of these two. Specifically, I want to know if any sort of relation exists between $\...
- 1