Porter D, Wigton RS, Reidelbach MA, Bleich HL, SLACK WV.  1988.  Self-service computerized bibliographic retrieval: a comparison of Colleague and PaperChase, programs that search the MEDLINE data base.. Comput Biomed Res. 21(5):488-501.

Ryan P, Winand D, Bleich HL, SLACK WV, Porter D.  1987.  Computer searching of the medical literature.. Ann Intern Med. 106(1):168-9.

Safran C, Porter D, Rury CD, Herrmann FR, Lightfoot J, Underhill LH, Bleich HL, SLACK WV.  1990.  ClinQuery: searching a large clinical database.. MD Comput. 7(3):144-53.