Below charts are scatter plots of projects, with regression lines, without their outliers removed. (Removing outliers does not improve correlation.)
All projects show different phases as separate points. The “Phases grouped” chart shows multiple phases of a project as a single point with total Length, % of total tunnel length and weighted average of cost/km.
Hover over points for more info, zoom out to see the outliers. The charts have been cropped for easy comparison.
The scatter plots below show regressions within projects with phases grouped and ungrouped, those with 90% tunnels, with and without outliers. Ranges without outliers were determined based on Upper Bounds as (Quartile 3+ (3*Inter quartile range)), and Lower Bounds= 0, both for Length and Cost/km.
Click on key elements to isolate projects for each region.