Basic Epidemiology (48 mins)
Scroll down and read pages 51-59 in "Chapter 3: Types of studies" on the potential errors in epidemiological studies. Answer 'Study questions' 3.3, 3.4, and 3.7 found on page 60.
Click http://apps.who.int/iris/bitstream/handle/10665/43541/9241547073_eng.pdf link to open resource.