Using
one margin of error for multiple comparisons
To
avoid calculating a separate margin of error for each response category, it is common to
calculate the most conservative standard error of a proportion (p=.5) and use this to
represent the margin of error for all response options within a specific subgroup. In the table below, a separate margin of error is
calculated for the total sample, the male sample, and the female sample.
Summary
Table
Using
one confidence interval (CI) for all data in one subgroup
(Source: GSS: Random sample of 1496 US Adults in 1993) 





All 
Male 
Female 
Total
Count 
1496 
641 
855 
95%
CI (+/) 
2.5% 
3.9% 
3.4% 
Respondent's
highest degree 



<
High school 
18.6% 
19.5% 
18.0% 
High
school 
52.1% 
47.4% 
55.7% 
Junior
college 
6.0% 
5.8% 
? 6.2% 
Bachelor 
15.6% 
16.8% 
14.7% 
Graduate 
?
7.6% 
10.5% 
? 5.4% 
I am 95% confident the percent of U.S. adults
with a junior college education level is between 3.5% and 8.5% (6.0% +/ 2.5%).
? I am 95% confident the percent of Female U.S.
adults with a junior college education level is between 2.8% and 9.6% (6.2% +/ 3.4%).
?
I am 95% confident the percent of U.S. adults
with a graduate education level is between 5.1% and 10.1% (7.6% +/ 2.5%).
?
I am 95% confident the percent of U.S. adults
with a graduate education level is between 2.0% and 8.8% (5.4% +/ 3.4%).
