11 questions linked to/from How to 'sum' a standard deviation?
140k views

### Does the variance of a sum equal the sum of the variances?

Is it (always) true that $$\mathrm{Var}\left(\sum\limits_{i=1}^m{X_i}\right) = \sum\limits_{i=1}^m{\mathrm{Var}(X_i)} \>?$$
28k views

### Standard Deviation After Subtracting One Mean From Another

I've got two sets of data from some fluorescent cells. The first set is when the cells don't have their fluorescence switched on, but they are still faintly glowing. The second set is when they do ...
5k views

### “Averaging” variances

I need to obtain some sort of "average" among a list of variances, but have trouble coming up with a reasonable solution. There is an interesting discussion about the differences among the three ...
599 views

### Calculating standard deviations for aggregated means

Example: Say I have a normal distribution that contains responses from both male and female participants with an average score of 50 ± 2. Lets then say I actually receive this information in the ...
340 views

### “Average” standard errors of multiple samples

let's assume that I have 3 subjects with each of them producing 5 values. Now, I can calculate the mean, variance, standard deviation, and standard error for each subject. Each subject has its own ...
406 views

### Sample standard deviation or population standard deviation

I'm running an A/B testing in a website and I'm capturing the number of clicks in a given area of a page. I am calculating the average of clicks per user's session and its standard deviation. The ...
398 views

### Calculate AttrakDiff confidence rectangle

I evaluated an app on attrakdiff.de where I got this chart. It shows PQ and HQ. It ranges in both directions from -3 to +3. In the chart is a point (PQ, HQ) which is surrounded by a confidence ...
202 views

### Average of values, their standard deviations and ranges

After reading for hours, I am still swimming. I have a set of plasma concentration results from different labs: ...
197 views

### Sum of Variance or Standard Error?

My end goal is to present the average travel time for a corridor and the standard deviation (or standard error) of that travel time. I'm not sure what to present to be statistically correct, here is ...
here's the thing I've trying to wrap my head around. Please point out any error in reasoning. Imagine you want to estimate the number of people in a field of known total area ($A_{T}$). People are ...