Which research method provides the best way of assessing whether cigarette smoking boosts mental alertness?

The answer is "the experiment".

An experiment is a method completed to support, discredit, or approve a hypothesis. Experiments give understanding into circumstances and end results by exhibiting what result happens when a specific factor is controlled. Experiments differ significantly in objective and scale, yet dependably depend on repeatable method and coherent examination of the outcomes. There additionally exists regular exploratory examinations.