There are a load of discussions online about adding means and recalculating the standard deviation, but on ...

If you add the "local" variances together, it will be very small compare to the "global" variance. You cannot predict the variance of the year using variance of 2 half year. So, in the accepted answer, while the sum calculation is correct, the division by 12 to get the monthly number means nothing.. Of the three sections, the first and last ...

2015年1月13日 · So what we see is that you certainly can calculate the mean of the means, but the mean of the means and the mean of all the raw data don't match. We can also try a weighted average using @BilltheLizard's suggestion to use each group's sample size as a weight (the weights are indicated with the w argument):

2018年1月18日 · So as you can see, the actual mean of the whole sample is a weighted average of the sample means of the subgroups (where each weight is proportionate to the size of the subgroup). Consequently, if you take a set of subgroups of unequal size, and you take the straight (unweighted) mean of their means, this will not generally be equal to the ...

I had the same problem: having the standard deviation, means and sizes of several subsets with empty intersection, compute the standard deviation of the union of those subsets. I like the answer of sashkello and Glen_b ♦, but I wanted to find a proof of it. I did it in this way, and I leave it here in case it is of help for anybody.

2013年3月6日 · In the case of k-means you compute the euclidean distance between each observation (data point) and each cluster mean (centroid) and assign the observations to the most similar cluster. Then, the label of the cluster is determined by examining that average characteristics of the observations classified to the cluster relative to the averages of ...

I read about pooled variance, but this is not depending on the means of the subsets and can't therefore possibly be true, since the spacing of the two "subgaussians" is obviously of influence. [EDIT] As a matter of fact, there is! How to calculate pooled variance of two groups given known group variances, means, and sample sizes? I apologize.

2017年8月1日 · I have multiplied together two means and now want to calculate the overall standard deviation. The two means and standard deviation are here: 13.7 +/- 12.7 (1SD) and 4.0 +/- 2.6 (1SD). So the answer would be 55.11 with what overall standard deviation? I then want to multiply this answer of 55.1 by 92.

2018年12月30日 · $\begingroup$ Take the 84 data points and ignore the time. calculate the mean and SD for the 84 combined. Let me assume, for example, you want average weight and height (perhaps to calculate average BMI and its SD?) based …

2015年11月24日 · K-means is a least-squares optimization problem, so is PCA. k-means tries to find the least-squares partition of the data. PCA finds the least-squares cluster membership vector. The first Eigenvector has the largest variance, therefore splitting on this vector (which resembles cluster membership, not input data coordinates!) means maximizing ...