Exercises 1–4: experiments
two studies are described below. one is an observational study, while the other is an experiment.
study a:
a new dog food, specially designed for older dogs, has been developed. a veterinarian wants to test this new food against another dog food currently on the market to see if it improves
dogs’ health. thirty older dogs were randomly assigned to either the "new" food group or the "current" food group. after they were fed either the "new" or "current" food for six months,
their improvement in health was rated.
study b:
the administration at a large school wanted to determine if there was a difference in the mean number of text messages sent by ninth-grade students and by eleventh-grade students
during a day. students in a random sample of 30 ninth-grade students were asked how many text messages they sent per day. students in another random sample of 30
eleventh-grade students were asked how many text messages they sent per day. the difference in the mean number of texts per day was determined.