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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%

Interpretation

   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%).


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