DiTrapani J, Rockwood N, Jeon M. Explanatory IRT analysis using the SPIRT macro in SPSS. TQMP. 2018;14(2):81-98. doi: 10.20982/tqmp.14.2.p081
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.