In which of the following situations would it be most appropriate to conduct an experiment rather than an observational study?
The principal at a local high school wants to know if teachers in the school tend to call on boys more often than girls when asking questions in class.
A medical researcher wants to investigate how the average number of cigarettes someone smokes per week is related to the average medical costs that the individual incurs in one year.
A researcher wants to know if elementary school students who are physically bullied are more likely to become bullies in middle school.
A developmental psychologist is interested in knowing how different room temperatures affect a preschooler's ability to complete a series of tasks involving fine motor skills.
A nutritionist has noticed that healthier foods often cost more than less healthy alternatives. She wants to investigate if lower levels of family income are related to higher levels of childhood obesity.