Do Children Need Sleep to Grow? Aboutof a child's growth hormone is secreted during sleep, so it is believed that a lack of sleep in children might stunt growth.^{1 1}Rochman, B., "Please, Please, Go to Sleep",Timemagazine, March 26, 2012, p. 46.

1. What is the explanatory variable in this association?

(B)What is the response variable in this association?

(c) Describe a randomized comparative experiment to test this association.

(d) Explain why it is difficult (and unethical) to get objective verification of this possible causal relationship.