A study was conducted to determine whether early adenotosillectomy provides improved outcomes for children with sleep apnea. Adenotosillectomy is surgery to remove the tonsils and adenoids. The study recruited 453 children, 5 to 9 years of age, with obstructive sleep apnea syndrome and randomly assigned 226 children to early adenotosillectomy and the remaining 227 children to a strategy of watchful waiting. Symptoms of obstructive sleep apnea were assessed using the Pediatric Sleep Questionnaire sleep-related breathing disorder scale, with scores ranging from 0 to 1, with higher scores indicating greater severity. After 7 months, children in the early adenotosillectomy group had significantly greater reduction in symptoms than those in the watchful waiting group.

What is the response variable in this study?

a)The Pediatric Sleep Questionnaire sleep-related breathing disorder scale

b)The use of randomization and the fact that this was a comparative study

c)The treatment that children received

d)The 453 children with obstructive sleep apnea