Mueller and Oppenheimer (2014) conducted a series of studies comparing the effectiveness of taking classroom notes on laptops versus writing longhand. In one study, students were instructed to use their normal classroom note-taking strategy using either a notebook or a laptop while they watched a brief lecture. A short time later, the students were given a quiz on the lecture material. Although the quiz results showed no difference between the two strategies for factual questions, the students using longhand had significantly higher scores for conceptual questions. Explain why the researchers cannot conclude that taking longhand notes causes better conceptual learning than taking notes on a laptop.