- #1

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I have a set of records with the following data for each record: interval, mean speed, standard deviation of speed, number of observations. Exempli gratia:

Code:

```
1, 77.2, 1.75, 10
2, 75.9, 2.05, 12
```

- Thread starter KThy
- Start date

- #1

- 2

- 0

I have a set of records with the following data for each record: interval, mean speed, standard deviation of speed, number of observations. Exempli gratia:

Code:

```
1, 77.2, 1.75, 10
2, 75.9, 2.05, 12
```

- #2

mathman

Science Advisor

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- #3

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Right, of course. As I said, embarrasingly simple - thanks!Combine the second moments by the same procedure you used for the means. Finally calculate the std. dev. from the weighted mean and weighted second moment.

- #4

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However, for me the problem is that some of the intervals used for measuring average speed are different lengths of time. I believe the problem is the same?

Since we consider the data to be a

http://en.wikipedia.org/wiki/Mean_square_weighted_deviation

Cheers.

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