Main effects plot for prostate cancer. The plot on the left demonstrates search activity for each month, where each point is the average of all values for a particular month across all years, e.g. point 1 is the average search activity for January across all years. The plot on the right shows the effect of year, where each point is the average search activity for a particular year.
Glynn et al. BMC Cancer 2011 11:442 doi:10.1186/1471-2407-11-442