Freshman , revisited In Exercise 6 you thought about how to design a study to see if its true that students tend to gain weight during their first year in college. Well, Cornell Professor of Nutrition David Levitsky did just that. He recruited students from two large sections of an introductory health course. Although they were volunteers, they appeared to match the rest of the freshman class in terms of demographic variables such as sex and ethnicity. The students were weighed during the first week of the semester, then again 12 weeks later. Based on Professor Levitskys data, estimate the mean weight gain in first-semester freshmen and comment on the freshman 15. (Weights are in pounds.)

Variation of sample mean: With a population standard deviation of σ , the variation of the sample means is σX´ , which the standard deviation of the sample mean: σX= σ √n But if we don’t know the population standard deviation, σ , we use the sample standard deviation, S, to approximate the population standard deviation, and the variation of sample means becomes the standard error of the sample mean: S SEX= √ n In general, as long as outcomes of each trial are independent and from a fixed population (random & no replacement or large population relative to sample), then variation of sample ratio is inversely proportional to square root of sample size: