Raghunathan K, Layton JB, Ohnuma T, Shaw AD. Observational research using propensity scores. Adv Chronic Kidney Dis. 2016 Nov;23(6):367-72. doi: 10.1053/j.ackd.2016.11.010
Vickers AD, Palmer SCF. The influence of canopy cover and other factors upon regeneration of Scots pine and associated ground flora within Glen Tanar NNR. Forestry (Lond). 2000;73(1):37-49.