I need to know how to calculate the average for 2 different sets of data

[rayted]

Hi guys,

OCT NOV DEC

818	567	868
463	321	463

FIRST ROW: DEVICES
SECOND ROW: PEOPLE

Hi guys, if I want to know the average number of devices per person, how should I do this? Can someone please tell me the calculation? Is it the same to do it for each month or all 3 months together?

Thank you

 

[Steven G]

Hi guys,

OCT NOV DEC

818	567	868
463	321	463

FIRST ROW: DEVICES
SECOND ROW: PEOPLE

Hi guys, if I want to know the average number of devices per person, how should I do this? Can someone please tell me the calculation? Is it the same to do it for each month or all 3 months together?

Thank you

Well it seems to make no sense to find the average of 1 month, as the average of 1 number is itself.

I would calculate device/people for each month. Can you now find the average?

 

[j-astron]

Hi guys,

OCT NOV DEC

818	567	868
463	321	463

FIRST ROW: DEVICES
SECOND ROW: PEOPLE

Hi guys, if I want to know the average number of devices per person, how should I do this? Can someone please tell me the calculation? Is it the same to do it for each month or all 3 months together?

Thank you

Nope, you'll find that you get a different answer for each of the monthly ratios, vs taking an overall average over three months. Call the device numbers you have d1, d2, and d3, and the person counts you have p1, p2, and p3.

If you average the three monthly ratios, you might get something close to, but still not the same as, the overall average. Because, in general:

\(\displaystyle \displaystyle \frac{1}{3}\left(\frac{d_1}{p_1} + \frac{d_2}{p_2} + \frac{d_3}{p_3}\right) \neq \left(\frac{d_1+d_2+d_3}{p_1+p_2+p_3}\right) \)

EDIT: So you need to go and find out which average you are being required to report.

 

[Dr.Peterson]

OCT NOV DEC

818	567	868
463	321	463

FIRST ROW: DEVICES
SECOND ROW: PEOPLE

Hi guys, if I want to know the average number of devices per person, how should I do this? Can someone please tell me the calculation? Is it the same to do it for each month or all 3 months together?

As I understand it, you are asking whether to find the ratio for each month and then average them, or to add each row over all months and find the ratio of that.

The first is (818/463 + 567/321 + 868/463)/3 = (1.77 + 1.77 + 1.87)/3 = 1.803; the second is (818 + 567 + 868)/(463 + 321 + 463) = 2253/1247 = 1.807.

Both numbers make sense; but they are different, and have different meanings. In this case, the results are not very different, because the ratio does not change much. If that is typical, then it doesn't matter which way you do the calculation.

The first way is the average of the ratio; it is appropriate if what happens each month is significant. The second way is the overall ratio, and is particularly appropriate if the numbers for each month represent different parts of one bigger population (no overlap expected), so that your ratio will represent that combined population as a whole.

Possibly if I knew more about the people and the devices, and what makes them vary from month to month, I could make a judgment between the two calculations. As it is, it's too abstract.