Mean = np = 15(0.9) = 13.5 g. What is the standard deviation of the number of students who own a cell phone in simple random samples of 15 students? ඥ15(0.9)(1 − 0.9) = 1.16
8. For the following descriptions, list experimental units (or subjects), factors, levels, treatments, and response variables. 1. Veterinarians are interested in finding out which brands of dog food cause dogs to gain the most weight. Sixteen dogs younger than 5 and sixteen dogs older than 5 are selected and given either Science Diet, Pedigree, Alpo, or Purina. Factors: age brand Levels: greater than 5, less than 5; SD, Pe, A, Pu Treatments > 5 SD, > 5 Pe, > 5 A, > 5 Pu, < 5 SD, < 5 Pe, < 5 A, < 5 Pu Response variable: weight 2. A forester wants to know which of three types of tree (palm, pine, oak) does best resisting hurricane force winds. He selects 10 pieces of wood from each type of tree and subjects it to hurricane force winds. He then records the level of damage for each type of wood on a scale from 1 to 10. Factors: type of tree Levels: palm, pine, oak Treatments: palm, pine, oak Response variable: level of damage on a scale of 1 to 10 3. A corporate manager is interested in finding the best way to improve productivity. He wants to see if reading a book or not or attending a seminar or not has the most impact on productivity. He assigns the treatments to 8 branches of his company. Factors: book seminar Levels: read a book, didn’t read a book; attended seminar, didn’t attend seminar Treatments: book and seminar, book and no seminar, no book seminar, no book and no seminar Response Variable: productivity SD Pe > 5 A Pu < 5 SD Pe A Pu pine palm oak seminar book no seminar seminar no book no seminar
4. Doctors are interested in determining whether fitness level (low, average, high) and age (20’s, 30’s, 40’s, 50’s) impact time to recovery after knee surgery. 40 people of various ages and fitness levels are evaluated for time to recovery. Factors: fitness level age Levels: low average high 20 30 40 50 treatments: Lo20, Lo30, Lo40, Lo50, Av20, Av30, Av40, Av50, Hi20, Hi30, Hi40, Hi50 response variable: time to recovery 9. Read the following descriptions, and tell what source of bias(es) each represents (undercoverage, non-response, response bias, or poor wording of questions). 1. A mail survey is conducted to determine what percentage of Americans are vegetarian or vegan. 15% of households respond. Non-response 2. We would like to have an estimate of the percentage of people that participate in illegal drugs. We call 3,500 households. In the study, no one says that they do illegal drugs. Response bias 3. How many Americans are supportive of welfare programs? To find the answer, we will ask “Given the failure of welfare in the US, do you feel welfare programs should be eliminated?” poor wording in a question How can this question be reworded so as not to cause bias? Should the welfare program be continued or eliminated?