Basic Epidemiology (17 mins)
Scroll down to "Chapter 2: Measuring Health and Disease" and read the section titled "Comparing Disease Occurrence" on pages 34 to 35 and answer 'Study questions' 2.4 and 2.5.
Click http://apps.who.int/iris/bitstream/handle/10665/43541/9241547073_eng.pdf link to open resource.