Data collected by Dixon and Massey contains measurements of the cholesterol levels of 20 randomly selected individuals measured both in 1952 and then again in 1962. A researcher wanted to see if the cholesterol levels increase as people get older. Which hypothesis test should be used? One mean (sigma known) One mean (sigma unknown) Mean of differences, using dependent samples (paired data). Difference of two means (independent samples) Several means (ANOVA) One proportion Difference of two proportions Chi-Square test for independence