Assignment One

  1. The data set guinea-pigs.data gives the survival times of 72 guinea pigs after injection with tubercle bacilli in a medical experiment.
    1. Give a 95 percent confidence interval for the mean survival time.
    2. Check the data graphically and numerically for outliers, or anything else untoward. Report what you see. (Yes, you should ordinarily do this first, but that disrupts the flow of this problem.)
    3. Take the logarithm of the data (use the log command in R) and repeat the checks above.
    4. Give a 95 percent confidence interval for the mean log survival time and transform this (use the exp command in R) back to an interval of untransformed units (i.e. undo the logarithm).
  2. The dataset spanish-test.data gives pre-test and post-test scores on the MLA listening test in Spanish for 20 high school spanish teachers who attended an intensive summer course in Spanish. Does attending the institute improve listening skills?
    1. Check the data graphically and numerically for outliers or anything else untoward. Report what you see.
    2. Give a 90 percent confidence interval for the mean increase in test score.
    3. State appropriate null and alternative hypotheses for a hypothesis test.
    4. Carry out your hypothesis test and report the p-value.
  3. The data set study-habits.data gives results for students at a selective private college on the Survey of Study Habits and Attitudes (SSHA), a psychological test designed to measure the motivation, attitudes, and study habits of college students. Most studies have found that the mean SSHA score is lower for men than that for women.
    1. Again check the data graphically and numerically for outliers or anything else untoward. Report what you see.
    2. Do these data support the claim that the mean SSHA score is lower for men than for women? (Use both a confidence interval and a hypothesis test to answer this question.)