It is really helpful to start reading professional research articles to see how these concepts are used in actual study scenarios. Give it a try in this article, where the researchers examined the relationship between patients’ perception about coffee consumption and distress symptoms in patients with inflammatory bowel disease: Barthel, C. Wiegand, S., Scharl, S., et al. (2015). Patients’ perception on the impact of coffee consumption in inflammatory bowel disease: Friend or foe? A patient survey. Nutrition Journal, 14(78). doi:10.1186/s12937- 015-0070-8.

How many patients with Crohn’s disease (CD) responded to the survey? Were they all included in the study?