Read the paragraph and answer the questions that follow:

In the research article titled "The Impact of Sleep Quality on Cognitive Performance in University Students," various types of research variables were meticulously defined and analyzed. The independent variable in this study was sleep quality, measured through self-reported measures on the Pittsburgh Sleep Quality Index (PSQI). The dependent variable was cognitive performance, assessed via a series of standardized neuropsychological tests. Control variables, such as age, gender, and academic workload, were accounted for to minimize their potential confounding effects on the observed relationship. The study also identified potential extraneous variables, including caffeine intake and stress levels, which were monitored to ensure they did not inadvertently impact the results. By systematically managing these variables, the researchers were able to draw more accurate conclusions about the influence of sleep quality on cognitive abilities, thus contributing valuable insights to the field of educational psychology.