Alexander, JM «Randomized controlled trial of breast shells and Hoffman's exercises for inverted and non-proctractile nipples» (en anglès). British Medical Journal, 304(6833), 4-1992, pàg. 1030–2. DOI: 10.1136/bmj.304.6833.1030. PMC: 1881748. PMID: 1586788.
Alexander, JM «Randomized controlled trial of breast shells and Hoffman's exercises for inverted and non-proctractile nipples» (en anglès). British Medical Journal, 304(6833), 4-1992, pàg. 1030–2. DOI: 10.1136/bmj.304.6833.1030. PMC: 1881748. PMID: 1586788.