Basic Epidemiology (8 mins)
Scroll down to "Chapter 11: First Steps in Practical Epidemiology" and read the section titled "Critical Reading" (pages 178-181). Answer 'Study questions' 11.1 and 11.2.
Click http://apps.who.int/iris/bitstream/handle/10665/43541/9241547073_eng.pdf link to open resource.