Research published in the journal Cough in 2012 examined the records of 241 children who visited a pediatrician with a severe cough. They found that coughing stopped in 47% of the 101 children who were treated with the non-opiate cough suppressant levodropropizine compared with 28% of the 60 children treated with cough suppressants containing opiates and 20% of the 80 children who were not prescribed anything for their coughs. The difference in cough relief was found to be statistically significant. However, in reviewing the study a critic pointed out that pediatricians are known to be hesitant to prescribe opiate based cough suppressants in very young children except in very specific medical circumstances.

In this situation:

the treatment was the explanatory variable and whether the child stopped coughing is the response variable.

the treatment was the response variable and whether the child stopped coughing is the explanatory variable

the medical circumstances affecting what is prescribed was the response variable and whether the child stopped coughing was the explanatory variable.

the medical circumstances affecting what is prescribed was the response variable and the treatment was the explanatory variable.