What are the controlled variables of this study httpswwwncbi

What are the controlled variables of this study?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2800819/

Solution

The study is about analgesic effects produced by intrathecal morphine administration in individuals with spinalcord injury affecting the locomotary function. The controlled variables are the dose of morphine (0, 30, or 90 g). The independent variable is the effects produced by the morphine administration and lesion size. The side effects produced by morphine administration in individuals with spinalcord injuries had shown great impact on recovery and resulted in increase of the neuropathic pains.