• #### Adding averages - I'm confused

From rithykat@gmail.com@21:1/5 to All on Sat Jan 18 12:04:00 2020
On Tuesday, July 28, 2009 at 5:08:21 PM UTC-7, Walt987 wrote:
I've been told it is reasonable to add the averages of several groups to get the "total mean" (for lack of a better word) of the groups. For example you could add the average abundance of several species of fish to get a total abundance value for all

1) Does it make sense and if so could someone explain in words what it means and how it is used?
2) Is there a term for this value?
3) I found a procedure on a web page for calculating the standard deviation (not additive) of this value but this raised a new question - how does it make sense to have a standard deviation for a total?
4) If it makes sense so far, is there a way to calculate standard error for this value?
5) If this value is not a mean, can it be used in statistical tests?

Thanks for any help.

If you own a store and the average cost of the shoes you buy to stock your store is \$50 and the average cost of the clothes you buy for your store is \$46 then the total average cost of the clothes AND shoes you buy for the store is \$50+\$46=\$96. (This is
the case where you can add averages.)

You cannot add averages if for example your one class got an average of 50% on their test and you have another class that got 75% on their test, you can't add their averages and say the combined average for your two classes is 50% +75%=125%. (It doesn't
make sense to add averages in this case)

Let me know what you think...

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• From Rich Ulrich@21:1/5 to rithykat@gmail.com on Sat Jan 18 19:37:41 2020
On Sat, 18 Jan 2020 12:04:00 -0800 (PST), rithykat@gmail.com wrote:

On Tuesday, July 28, 2009 at 5:08:21 PM UTC-7, Walt987 wrote:
I've been told it is reasonable to add the averages of several groups to get the "total mean" (for lack of a better word) of the groups. For example you could add the average abundance of several species of fish to get a total abundance value for all

1) Does it make sense and if so could someone explain in words what it means and how it is used?
2) Is there a term for this value?
3) I found a procedure on a web page for calculating the standard deviation (not additive) of this value but this raised a new question - how does it make sense to have a standard deviation for a total?
4) If it makes sense so far, is there a way to calculate standard error for this value?
5) If this value is not a mean, can it be used in statistical tests?

Thanks for any help.

If you own a store and the average cost of the shoes you buy to stock your store is \$50 and the average cost of the clothes you buy for your store is \$46 then the total average cost of the clothes AND shoes you buy for the store is \$50+\$46=\$96. (This is
the case where you can add averages.)

You cannot add averages if for example your one class got an average of 50% on their test and you have another class that got 75% on their test, you can't add their averages and say the combined average for your two classes is 50% +75%=125%. (It doesn't
make sense to add averages in this case)

Let me know what you think...