Name: Jim

Who is asking: Other Level: All

Question:
If a survey was completed by four different groups of people as indicated below what would the over-all margin of error be for this survey given the fact that the number of people in each group were different?

Group	# polled	Margin of error
A.	    779	          +/- 4%
B.	    315	          +/- 7%
C.	    323	          +/- 6%
D.	    254	          +/- 9%

Any help in solving this equation will be greatly appreciated.

It depends on the parameter you are estimating. We usually use margin of error for the estimation of a mean, so some "linear" operation will be suitable. I suggest to use weigted avarage:

over-all margine error
=(779*.04 + 315*.07 + 323*.06 + 254*.09)/(779+315+323+254).

Multiply the answer of this expression by 100 in order to get percents (%).