Principles of epidemiology course

The Centers for Disease Control and Prevention have a self-study course covering basic principles and applications of epidemiology.

The objectives as described in the full-text of the course materials:
- Describe key features and applications of descriptive and analytic epidemiology.
- Calculate and interpret ratios, proportions, incidence rates, mortality rates, prevalence, and years of potential life lost.
- Calculate and interpret mean, median, mode, ranges, variance, standard deviation, and confidence interval.
- Prepare and apply tables, graphs, and charts such as arithmetic-scale line, scatter
diagram, pie chart, and box plot.
- Describe the processes, uses, and evaluation of public health surveillance.
- Describe the steps of an outbreak investigation.

I haven't worked my way through the whole course yet but it has a great overview of the history of epidemiology and a good description/comparison of the various terms used in epidemiology (e.g. contrasting the various measures of risk, common techniques employed in epidemiology), and how to interpret illustration types commonly used in epidemiology papers (e.g. scatterplots, box plots).