All Couples	Endogamous Couples	Interracial Couples
Marriage Duration in Years	12.500	12.619	10.449
	(6.950)	(7.000)	(5.914)
Region of Residence
Midwest	0.264	0.271	0.159
Northeast	0.184	0.187	0.138
South	0.350	0.353	0.303
West	0.203	0.189	0.401
N	23,139	21,547	1,592

1. What proportion of all couples in the data represented in the data that Dr. Zhang and Dr. Van Hook analyze are interracial?
2. Calculate the 95% confidence interval for the sample proportion that you calculated in part (a).
3. Calculate the 95% confidence interval for the average number of years that couples stayed married for endogenous couples.
4. Calculate the 95% confidence interval for the average number of years that couples stayed married for interracial couples.