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
Watts (Wideman) K, McAvinchey G, Quiroz R. Language services in survey research. ATA Chronicle. 2002 Jul;31(7):36-7.