Take another look at the two studies described above: study a (the dog food study) and study b (text messages). the
term random sample implies that a sample was randomly selected from a population. the terms random selection and
random assignment have very different meanings.
random selection refers to randomly selecting a sample from a population. random selection allows generalization to a
population and is used in well-designed observational studies. sometimes, but not always, the subjects in an experiment
are randomly selected.
random assignment refers to randomly assigning the subjects in an experiment to treatments. random assignment
allows for cause-and-effect conclusions and is used in well-designed experiments.
in study b. the data were collected from two random samples of students.
5. can the results of the survey be generalized to all ninth-grade and all eleventh-grade students at the school? why or
why not? discuss in detail.
6. suppose there really is a difference in the mean number of texts sent by ninth-grade students and by eleventh-grade
students. can we say that the grade level of the students is the cause of the difference in the mean number of texts
sent? why or why not? discuss the answer in detail.