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
Pueschel SM, Rothman KJ, Ogilby JD. Birth weight of children with down's syndrome. Am J Ment Defic. 1976 Jan;80(4):442-5.