Marcus reported on a study that treated children who had sleep apnea. Sleep apnea interferes with breathing while the child is asleep. Read the excerpts from the abstract, and answer the questions that follow it. (Adenotonsillectomy is surgery to remove the tonsils and adenoids.)
We randomly assigned 464 children, 5 to 9 years of age, with the obstructive sleep apnea syndrome to early adenotonsillectomy or a strategy of watchful waiting..There were significantly greater improvements in behavioral, quality-of-life, and polysomnographic [sleep study] findings and significantly greater reduction in symptoms in the early-adenotonsillectomy group than in the watchful-waiting group..
a. Was the study a controlled experiment or an observational study? Explain how you know.
b. Assuming that the study was properly conducted, can we conclude that the early surgery caused the improvements? Explain.