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
Edwards PET, Parsons GR, Myers KH. The economic value of viewing migratory shorebirds on the Delaware Bay: an application of the single-site travel cost model using on-site data. Hum Dimens Wildl. 2011;16(6):435-44. doi: 10.1080/10871209.2011.608180