Determine the sampling plan used in each of the following studies:

(a) In a study on head injuries reported in the article “Helmet use and risk of head injuries in Alpine skiers and snowboarders” published in the Journal of the American Medical Association (Sulheim et al., 2005), the author sampled every 10th skier in line at the ski lifts at a ski resort every Wednesday and Sunday during the winter months.

(b) In a study on the hepatitis B and C viruses reported in the article “Frequency of vaccine-related and therapeutic injections—Romania, 1998” published in the Morbidity and Mortality Weekly Report (1998) the authors sampled 300 households and surveyed each of the residents in a household.

(c) In a study on secondhand smoking reported in the article “Exposure to secondhand smoke among students aged 13–15 years—worldwide, 2000–2007”

published in the Morbidity and Mortality Weekly Report (2007), the authors collected sample data from participating schools by randomly selecting classes within a school and then surveying each of the students in the class.

(d) In a study of tuberculosis reported in the article “Tuberculin skin test screening practices among US colleges and universities” published in the Journal of the American Medical association (Hennessey et al., 1998), the authors randomly selected and surveyed 263 2-year colleges and 361 4-year universities.