In a study of the relationship between birth order and college success, an investigator found that 140 in a sample of 200 college graduates were firstborn or only child. In a sample of 120 non-graduates of comparable age and socioeconomic background, the number of firstborn or only child was 66. Estimate the difference between the proportions of firstborn or only child in the two populations from which these samples were drawn using a 90% confidence interval and interpret your results.