Which of the following is an example of “presence versus absence” variation of the independent variable?
All participants’ reaction times are measured after ingesting two beers.
In a study of distraction on reading comprehension, one group is distracted by noise, another by flashing light, and a third by a bad odor.
The control group gets no tutoring, one experimental group gets 15 min of tutoring a day, and a second experimental group gets 30 min of tutoring a day.
An experimental group receives guided notes and the control group does not receive guided notes.
