3.3
This is an observational study, as no treatment was imposed (i.e., people weren’t randomly assigned to use cell phones or not use cell phones). The explanatory variable is cell phone use, and the response variable is brain cancer status.
3.4
a. This is an observational study, as no
treatment was imposed (i.e., children weren’t randomly assigned to watch a
certain amount of television). The explanatory variable is time spent watching
TV as a child, and the response variable is level of aggressive behavior later
in life.
b. Children who watch a lot of TV may have other
variables in common (e.g., less guidance from parents, less interaction with
peers, less study time). Because these other variables may also affect the
level of aggressive behavior later in life, it’s impossible to isolate the
effect of the TV watching.
3.7
a. In an observational study, data would simply
be collected on people with respect to their alcohol choice and their general
health. In an experiment, people would be randomly assigned to either drink
wine or drink beer, and then their health would be compared.
b. People who drink wine (as opposed to beer)
may be wealthier, more educated, and may have
different eating habits. All of these variables could also impact a person’s
health.