In the described experiment, the level of nicotine is the independent variable, actively manipulated by the researcher to observe its effect on driving performance, which is measured by the number of collisions.
In the experimental study described, the level of nicotine is the independent variable. This means it is the variable that the researcher actively manipulates to examine its impact on the dependent variable, which in this case, would be the number of collisions during the driving test. Little discussion is needed on what specific effects nicotine has to understand that within the context of this study, it stands as the factor being tested for its potential influence on driving ability.
Nicotine's pharmacological effects and health impacts are well documented. Among these effects, nicotine can influence the autonomic system and carries a risk for cardiovascular diseases. However, the actual impact of nicotine on specific psychomotor functions, such as driving, requires targeted research such as described in the student's question.