The total number of active herds (solid areas) and the total number of breakdowns (lines) in each year between 2002 and 2008, the broken lines correspond to the number of “new” breakdowns – the breakdowns that are included in these analyses. The dark grey area and lines correspond to areas that were in one year testing, above the dark grey area and corresponding lines those that were in 2 and 3 year testing areas, above those holdings that were in four year testing between 2002 and 2008. The top block and lightest grey lines are those that were excluded at that time due to being in four year testing but subsequently removed from the analysis for that particular year.
Bessell et al. BMC Veterinary Research 2012 8:51 doi:10.1186/1746-6148-8-51