Averaging averages

[Guest]

Howdy,

I work at a car dealership and we sell both Hondas and Toyotas. I've done a
survey with my customers who own cars. I did this to find out if people who
own Hondas are more satisfied than people with Toyotas.

I want to "average the averages" below to find out if Honda owners are more
happy than Toyota owners. Here's some sample data:

Honda
Product #votes Average satisfaction grade per vote
Civic 1,211 75%
Accord 811 82%
Del Sol 355 55%
Passport 561 55%

Toyota
Corolla 1,356 88%
Camry 334 36%
Supra 284 36%
Landcrser 5 36%

How would I average the averages? Would I use the SUMPRODUCT formula for
each set? In other words, if the Honda set was in columns A through C, I
would do this, right?

=SUMPRODUCT(C1:C4,B1:B4/SUM(B1:B4))

 

[Guest]

I don't like complicated forumlas like sumproduct. I would create a new
colum, and in it put the product of #votes*avg sat, for each row. Then, I
would sum this for each auto maker, and divide by the total responses. This
would give you the average you seek, and would give you a visual indicator of
which brand is influencing the stat.

 

[Guest]

=SUMPRODUCT(B1:B4,C1:C4)/SUM(B1:B4)

 

[Guest]

The expression "average of an average" is math heresy but your approach isn't
really doing that and is giving the correct answer so lets all go and buy a
Toyota who edge it by a full percentage point

Mike