History

Fact Explanation
Cyclical occurrence in a female of reproductive age Menstruation in normal fertile females happen in regular cycles. The length of a normal cycle is usually between 21 and 35 days. A cycle that comes in the length of less than 21 days is called epimenorrhea or polymenorrhea, whereas the length of more than 35 days is called oligomenorrhea. [1, 2, 3, 4] The first half of each cycle is known as the follicular phase. In this phase, few ovarian follicles start to develop from one ovary under the influence of pituitary gonadotrophins. During the intercycle rise of follicle-stimulating hormone (FSH), selection of the dominant follicle takes place. At the same time, luteinizing hormone (LH) stimulates the synthesis of androgens, which serve as the substrate for the production of estrogens. Meanwhile other sex steroids are low. At ovulation luteinizing hormone and follicle-stimulating hormone surges are associated with falling estrogen levels, this is usually in the 14th day of the cycle. Secretions of progesterone and estrogen again are characteristic of the second half of menstruation or the luteal phase, which is followed by menstrual bleeding. [5, 6, 7, 8, 9, 10, 11]
Premenstrual syndrome It's a wide range of symptoms that happens in the second half of the menstruation and disappears after a day or two following the start of menstrual bleeding. The definite cause for this is unknown but it is hypothesized that the change in sex hormones during the second half of the menstrual cycle is responsible for it. The females feel vague symptoms of varying intensity. (i.e. bloating, headache, mood changes, constipation or diarrhea, fatigue) [12, 13, 14, 15, 16, 17]
Mid-cycle pain and bleeding Known as mittelshmerz, this brief unilateral mid-cycle pain is indicative of ovulation happening. There can be spotting associated with ovulation also. [18, 19, 20, 21, 22, 25, 26, 27]
Vaginal discharge The normal vaginal discharge is white, nonhomogeneous, and viscous. It contains vaginal squamous epithelial cells in a serous transudate, as well as material from sebaceous, sweat, and Bartholin's glands, and secretions from the cervix. Mucus spinnbarkeit, ferning, and wet weight are associated with the ovulatory phase of the menstrual cycle. The maximum mucus secretion is associated with ovulation. [28, 29, 30]
Menstrual bleeding The functional layer of the endometrium shows steroid hormone-dependent proliferation, differentiation, and shedding in the absence of the trophoblast. When the ovum is not fertilizede, menstrual bleeding is initiated by progesterone responsive decidual cells, and executed by PGE and PGF2α, vasoconstriction and matrix metalloprotease secretion by leukocytes. [7] The amount of mentrual fluid at each cycle should be less than 80 ml in volume, more than that is called menorrhagia. [31] The first menstrual bleeding is considered as the hallmark of a girl's puberty achievement. The first few menstrual cycles may not be regular, and they are usually anovulatory. [32] Irregularity of menstruation is observed also near menopause. [33]
References
  1. CREININ MITCHELL D., KEVERLINE SHARON, MEYN LESLIE A.. How regular is regular? An analysis of menstrual cycle regularity. Contraception [online] 2004 October, 70(4):289-292 [viewed 28 August 2014] Available from: doi:10.1016/j.contraception.2004.04.012
  2. PANIDIS D., TZIOMALOS K., CHATZIS P., PAPADAKIS E., DELKOS D., TSOURDI E. A., KANDARAKI E. A., KATSIKIS I.. Association between menstrual cycle irregularities and endocrine and metabolic characteristics of the polycystic ovary syndrome. European Journal of Endocrinology [online] December, 168(2):145-152 [viewed 28 August 2014] Available from: doi:10.1530/EJE-12-0655
  3. ALBERS J.R. et al. Abnormal Uterine Bleeding. Am Fam Physician. [online] 2004 Apr 15;69(8):1915-1926. [viewed 28 August 2014] Available from: http://www.aafp.org/afp/2004/0415/p1915.html
  4. KOUTRAS DEMETRIOS A.. Disturbances of Menstruation in Thyroid Disease. Ann NY Acad Sci [online] 1997 June, 816(1 Adolescent Gy):280-284 [viewed 28 August 2014] Available from: doi:10.1111/j.1749-6632.1997.tb52152.x
  5. OWEN JA JR. Physiology of the menstrual cycle. Am J Clin Nutr [online] 1975 Apr, 28(4):333-8 [viewed 29 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/1091131
  6. FARAGE MIRANDA A., NEILL SALLIE, MACLEAN ALLAN B.. Physiological Changes Associated with the Menstrual Cycle. Obstetrical & Gynecological Survey [online] 2009 January, 64(1):58-72 [viewed 29 August 2014] Available from: doi:10.1097/OGX.0b013e3181932a37
  7. MIHM M, GANGOOLY S, MUTTUKRISHNA S. The normal menstrual cycle in women. Anim Reprod Sci [online] 2011 Apr, 124(3-4):229-36 [viewed 29 August 2014] Available from: doi:10.1016/j.anireprosci.2010.08.030
  8. ECOCHARD R, GUILLERM A, LEIVA R, BOUCHARD T, DIREITO A, BOEHRINGER H. Characterization of follicle stimulating hormone profiles in normal ovulating women. Fertil Steril [online] 2014 Jul, 102(1):237-243.e5 [viewed 29 August 2014] Available from: doi:10.1016/j.fertnstert.2014.03.034
  9. RITCHIE W G. Sonographic evaluation of normal and induced ovulation.. Radiology [online] 1986 October, 161(1):1-10 [viewed 29 August 2014] Available from: doi:10.1148/radiology.161.1.3532176
  10. ECOCHARD R.. Side of ovulation and cycle characteristics in normally fertile women. [online] 2000 April, 15(4):752-755 [viewed 29 August 2014] Available from: doi:10.1093/humrep/15.4.752
  11. MESSINIS IE, MESSINI CI, DAFOPOULOS K. The role of gonadotropins in the follicular phase. Ann N Y Acad Sci [online] 2010 Sep:5-11 [viewed 29 August 2014] Available from: doi:10.1111/j.1749-6632.2010.05660.x
  12. RAPKIN AJ, AKOPIANS AL. Pathophysiology of premenstrual syndrome and premenstrual dysphoric disorder. Menopause Int [online] 2012 Jun, 18(2):52-9 [viewed 29 August 2014] Available from: doi:10.1258/mi.2012.012014
  13. RAPKIN ANDREA. A review of treatment of premenstrual syndrome & premenstrual dysphoric disorder. Psychoneuroendocrinology [online] 2003 August, 28:39-53 [viewed 29 August 2014] Available from: doi:10.1016/S0306-4530(03)00096-9
  14. YONKERS KIMBERLY ANN, O'BRIEN PM SHAUGHN, ERIKSSON ELIAS. Premenstrual syndrome. The Lancet [online] 2008 April, 371(9619):1200-1210 [viewed 29 August 2014] Available from: doi:10.1016/S0140-6736(08)60527-9
  15. DICKERSON LM, MAZYCK PJ, HUNTER MH. Premenstrual syndrome. Am Fam Physician [online] 2003 Apr 15, 67(8):1743-52 [viewed 29 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/12725453
  16. POTTER J, BOUYER J, TRUSSELL J, MOREAU C. Premenstrual syndrome prevalence and fluctuation over time: results from a French population-based survey. J Womens Health (Larchmt) [online] 2009 Jan-Feb, 18(1):31-9 [viewed 29 August 2014] Available from: doi:10.1089/jwh.2008.0932
  17. Premenstrual Syndrome. The Lancet [online] 1981 December, 318(8260-8261):1393-1394 [viewed 29 August 2014] Available from: doi:10.1016/S0140-6736(81)92805-1
  18. GUILLERMO CHRISALBETH J, MANLOVE HEIDI A, GRAY PETER B, ZAVA DAVID T, MARRS CHANDLER R. Female social and sexual interest across the menstrual cycle: the roles of pain, sleep and hormones. BMC Women's Health [online] 2010 December [viewed 29 August 2014] Available from: doi:10.1186/1472-6874-10-19
  19. GRAY J. 7 Abdominal pain, abdominal pain in women, complications of pregnancy and labour. Emergency Medicine Journal [online] 2004 September, 21(5):606-613 [viewed 29 August 2014] Available from: doi:10.1136/emj.2004.017830
  20. MARINHO AO, SALLAM HN, GOESSENS L, COLLINS WP, CAMPBELL S. Ovulation side and occurrence of mittelschmerz in spontaneous and induced ovarian cycles. Br Med J (Clin Res Ed) [online] 1982 Feb 27, 284(6316):632 [viewed 29 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1496249
  21. KROHN PL. Intermenstrual Pain (the "Mittelschmerz") and the Time of Ovulation Br Med J [online] 1949 May 7, 1(4609):803-805 [viewed 29 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2049988
  22. ADDINSELL AW. Mittelschmerz and Dysmenorrhoea Br Med J [online] 1902 Nov 1, 2(2183):1472 [viewed 29 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2402043
  23. SLOME J. Ovulation side and occurrence of mittelschmerz in spontaneous and induced ovarian cycles Br Med J (Clin Res Ed) [online] 1982 Apr 10, 284(6322):1114 [viewed 29 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1497907
  24. ALSINNAWI M, FLEMING FJ, KENNY BJ, WALDRON D. Clinical images. Atypical midcycle pain. Am J Surg [online] 2009 Jan, 197(1):e1-2 [viewed 29 August 2014] Available from: doi:10.1016/j.amjsurg.2007.12.065
  25. HANN LUCY E.. Mittelschmerz. JAMA [online] 1979 June [viewed 29 August 2014] Available from: doi:10.1001/jama.1979.03290510039024
  26. ABBOTT JASON. Optimal management of chronic cyclical pelvic pain: an evidence-based and pragmatic approach. IJWH [online] 2010 August [viewed 29 August 2014] Available from: doi:10.2147/IJWH.S7991
  27. DASHARATHY S. S., MUMFORD S. L., POLLACK A. Z., PERKINS N. J., MATTISON D. R., WACTAWSKI-WENDE J., SCHISTERMAN E. F.. Menstrual Bleeding Patterns Among Regularly Menstruating Women. American Journal of Epidemiology [online] December, 175(6):536-545 [viewed 29 August 2014] Available from: doi:10.1093/aje/kwr356
  28. KELLY K.G. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Chapter 179: Tests on Vaginal Discharge. [web] [viewed 29 August 2014] Available from: http://www.ncbi.nlm.nih.gov/books/NBK288/
  29. FEHRING RICHARD J. Accuracy of the peak day of cervical mucus as a biological marker of fertility. Contraception [online] 2002 October, 66(4):231-235 [viewed 29 August 2014] Available from: doi:10.1016/S0010-7824(02)00355-4
  30. FEHRING RICHARD J., SCHNEIDER MARY, RAVIELE KATHLEEN, BARRON MARY LEE. Efficacy of Cervical Mucus Observations Plus Electronic Hormonal Fertility Monitoring as a Method of Natural Family Planning. [online] 2007 February, 36(2):152-160 [viewed 29 August 2014] Available from: doi:10.1111/j.1552-6909.2007.000129.x
  31. REID P. C.. Assessment of menorrhagia by total menstrual fluid loss. J Obstet Gynaecol [online] 2006 January, 26(5):438-441 [viewed 31 August 2014] Available from: doi:10.1080/01443610600747215
  32. Menstruation in Girls and Adolescents: Using the Menstrual Cycle as a Vital Sign. PEDIATRICS [online] December, 118(5):2245-2250 [viewed 31 August 2014] Available from: doi:10.1542/peds.2006-2481
  33. BURGER HG, HALE GE, DENNERSTEIN L, ROBERTSON DM. Cycle and hormone changes during perimenopause: the key role of ovarian function. Menopause [online] 2008 Jul-Aug, 15(4 Pt 1):603-12 [viewed 31 August 2014] Available from: doi:10.1097/gme.0b013e318174ea4d

Differential Diagnoses

Fact Explanation
Vaginal bleeding due to other reeasons i.e. dysfunctional uterine bleeding (abnormal bleeding from the vagina that is due to changes in hormone levels, like anovulatory bleeding, menorrhagia, metrorrhagia, oligomenorrhea, polymenorhea), implantation bleeding, miscarriage are the commonest forms of bleeding in a female of fertile age that can be misdiagnosed as normal menstrual bleeding. Malignancies of the reproductive tract should be considered in suspicious instances. Post-menopausal bleeding should be considered as another entity. [1, 2, 3, 4, 5, 6]
References
  1. ALBERS JR, HULL SK, WESLEY RM. Abnormal uterine bleeding. Am Fam Physician [online] 2004 Apr 15, 69(8):1915-26 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/15117012
  2. MOLVI SHABA N., DASH KIRANBALA, RASTOGI HARSH, KHANNA SHAKTI B.. Transcatheter Embolization of Uterine Arteriovenous Malformation: Report of 2 Cases and Review of Literature. Journal of Minimally Invasive Gynecology [online] 2011 November, 18(6):812-819 [viewed 31 August 2014] Available from: doi:10.1016/j.jmig.2011.07.007
  3. SWEET MG, SCHMIDT-DALTON TA, WEISS PM, MADSEN KP. Evaluation and management of abnormal uterine bleeding in premenopausal women. Am Fam Physician [online] 2012 Jan 1, 85(1):35-43 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/22230306
  4. ALBERS JR, HULL SK, WESLEY RM. Abnormal uterine bleeding. Am Fam Physician [online] 2004 Apr 15, 69(8):1915-26 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/15117012
  5. FARRELL E. Dysfunctional uterine bleeding. Aust Fam Physician [online] 2004 Nov, 33(11):906-8 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/15584330
  6. BONGERS MARLIES Y., MOL BEN W.J., BRöLMANN HANS A.M.. Current treatment of dysfunctional uterine bleeding. Maturitas [online] 2004 March, 47(3):159-174 [viewed 31 August 2014] Available from: doi:10.1016/j.maturitas.2003.08.002

Investigations - for Diagnosis

Fact Explanation
Pituitary hormones The pituitary hormones that mainly affect the menstrual cycle are Lutenizing hormone (LH) and follicle stimulating hormone (FSH). At the start of the menstrual cycle, LH is low, FSH rises in a small but significant level at the end of the preceding cycle. This rise heralds the recruitment of secondary early antral follicles and the process whereby the dominant follicle will be selected for ovulation. At around the mid-cycle, there is a LH surge and a FSH increase as well, which causes ovulation. Following ovulation, the hormone levels drop. The hormone levels change with ethnicity and how close the female is to menarche or menopause. [1, 2, 3, 4]
Sex steroids Mainly the estradiol and progesterone. Estradiol reflects the secretory activity of the growing follicle, and its concentrations rise in parallel with follicular growth, reaching highest levels when the follicle achieves maturation. Progesterone reflects the secretory activity of the corpus luteum. It rises and falls in a characteristic 14-day bell-shaped curve representative of the finite life span of the corpus luteum. Estradiol is also secreted by the corpus luteum in a similar rise-and-fall fashion. [1,2,5,6,7,8]
Ultrasound follicular monitoring It is a simple assessment of ovarian follicles on regular intervals, to document the pathway to ovulation. Ultrasound monitoring begins on day 3 of cycle, to assess a baseline size, as well as exclude if any cyst remains from previous cycles, and count the number of existing follicles. On day 7 ovulatory dominant follicle can be identified. Once follicle reaches 16 mm size, a daily monitoring of follicle is recommended by the radiologists. Ovulation is sonographically determined by follicle suddenly disappearing or regressing in size, its irregular margins, intra-follicular echogenicity, free fluid in pouch of douglas and increased perifollicular blood flow velocities on doppler san. [9, 10, 11, 12, 13]
Day 21 progesterone levels Serum progesterone in days 21-23 of the menstrual cycle is used as a marker of ovulation. [14] [15]
References
  1. SHERMAN BM, KORENMAN SG. Hormonal characteristics of the human menstrual cycle throughout reproductive life. J Clin Invest [online] 1975 Apr, 55(4):699-706 [viewed 31 August 2014] Available from: doi:10.1172/JCI107979
  2. FERIN, M. The Hypothalamic-Hypophyseal-Ovarian Axis and the Menstrual Cycle. Glob. libr. women's med.,2008; [web] [viewed 31 August 2014] Available from: DOI 10.3843/GLOWM.10283 & http://www.glowm.com/section_view/heading/The%20Hypothalamic-Hypophyseal-Ovarian%20Axis%20and%20the%20Menstrual%20Cycle/item/282
  3. SHERMAN B M, KORENMAN S G. Hormonal characteristics of the human menstrual cycle throughout reproductive life.. J. Clin. Invest. [online] 1975 April, 55(4):699-706 [viewed 31 August 2014] Available from: doi:10.1172/JCI107979
  4. MARSH E. E., SHAW N. D., KLINGMAN K. M., TIAMFOOK-MORGAN T. O., YIALAMAS M. A., SLUSS P. M., HALL J. E.. Estrogen Levels Are Higher across the Menstrual Cycle in African-American Women Compared with Caucasian Women. The Journal of Clinical Endocrinology & Metabolism [online] 2011 October, 96(10):3199-3206 [viewed 31 August 2014] Available from: doi:10.1210/jc.2011-1314
  5. BAO AM, LIU RY, VAN SOMEREN EJ, HOFMAN MA, CAO YX, ZHOU JN. Diurnal rhythm of free estradiol during the menstrual cycle. Eur J Endocrinol [online] 2003 Feb, 148(2):227-32 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/12590642
  6. GANDARA BK, LERESCHE L, MANCL L. Patterns of Salivary Estradiol and Progesterone across the Menstrual Cycle Ann N Y Acad Sci [online] 2007 Mar:446-450 [viewed 31 August 2014] Available from: doi:10.1196/annals.1384.022
  7. MUMENTHALER MARTIN S., O'HARA RUTH, TAYLOR JOY L., FRIEDMAN LEAH, YESAVAGE JEROME A.. Relationship between variations in estradiol and progesterone levels across the menstrual cycle and human performance. Psychopharmacology [online] December, 155(2):198-203 [viewed 31 August 2014] Available from: doi:10.1007/s002130100700
  8. ROTHMAN MS, CARLSON NE, XU M, WANG C, SWERDLOFF R, LEE P, GOH VH, RIDGWAY EC, WIERMAN ME. Reexamination of testosterone, dihydrotestosterone, estradiol and estrone levels across the menstrual cycle and in postmenopausal women measured by liquid chromatography-tandem mass spectrometry. Steroids [online] 2011 Jan, 76(1-2):177-82 [viewed 31 August 2014] Available from: doi:10.1016/j.steroids.2010.10.010
  9. SKANDHAN A.K.P. et al. Follicular monitoring. [web] [viewed 31 August 2014] Available from: http://radiopaedia.org/articles/follicular-monitoring
  10. ATA B., SEYHAN A., REINBLATT S. L., SHALOM-PAZ E., KRISHNAMURTHY S., TAN S. L.. Comparison of automated and manual follicle monitoring in an unrestricted population of 100 women undergoing controlled ovarian stimulation for IVF. Human Reproduction [online] December, 26(1):127-133 [viewed 31 August 2014] Available from: doi:10.1093/humrep/deq320
  11. RAINE-FENNING N., JAYAPRAKASAN K., CLEWES J.. Automated follicle tracking facilitates standardization and may improve work flow. Ultrasound Obstet Gynecol [online] December, 30(7):1015-1018 [viewed 31 August 2014] Available from: doi:10.1002/uog.5222
  12. PAN PING, CHEN XIAOLI, LI YU, ZHANG QINGXUE, ZHAO XIAOMIAO, BODOMBOSSOU-DJOBO MADAFEITOM M. A., YANG DONGZI, BHATTACHARYA SANJOY. Comparison of Manual and Automated Measurements of Monodominant Follicle Diameter with Different Follicle Size in Infertile Patients. PLoS ONE [online] 2013 October [viewed 31 August 2014] Available from: doi:10.1371/journal.pone.0077095
  13. GIANNOPOULOS T, SHERRIFF E, CROUCHER CAROLYN. Follicle tracking of women receiving clomiphene citrate for ovulation induction. J Obstet Gynaecol [online] 2005 January, 25(2):169-171 [viewed 31 August 2014] Available from: doi:10.1080/01443610500041073
  14. WILCOX AJ, DUNSON D, BAIRD DD. The timing of the "fertile window" in the menstrual cycle: day specific estimates from a prospective study BMJ [online] 2000 Nov 18, 321(7271):1259-1262 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC27529
  15. BADAWY AHMED, STATE OMNIA, ABDELGAWAD SOMA. Array. Acta Obstet Gynecol Scand [online] 2007 January, 86(2):218-222 [viewed 31 August 2014] Available from: doi:10.1080/00016340601090337

Investigations - Fitness for Management

Fact Explanation
Hemoglobin count Since iron deficiency and resulting anemia is common among menstruating females. [1, 2, 3, 4, 5]
References
  1. HALLBERG L, ROSSANDER-HULTéN L. Iron requirements in menstruating women. Am J Clin Nutr [online] 1991 Dec, 54(6):1047-58 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/1957820
  2. KIM I, YETLEY EA, CALVO MS. Variations in iron-status measures during the menstrual cycle. Am J Clin Nutr [online] 1993 Nov, 58(5):705-9 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/8237879
  3. PEURANPää PIRKKO, HELIöVAARA-PEIPPO SATU, FRASER IAN, PAAVONEN JORMA, HURSKAINEN RITVA. Effects of anemia and iron deficiency on quality of life in women with heavy menstrual bleeding. Acta Obstet Gynecol Scand [online] December, 93(7):654-660 [viewed 31 August 2014] Available from: doi:10.1111/aogs.12394
  4. DE SOUZA SéRGIO SIMõES, CAMARGOS AROLDO F., FERREIRA MáRCIA CRISTINA FRANçA, DE ASSIS NUNES PEREIRA FRANCISCO, DE REZENDE CAROLINA PASSOS, ARAúJO CíCERO AUGUSTO ALVES, SILVA FILHO AGNALDO LOPES. Hemoglobin levels predict quality of life in women with heavy menstrual bleeding. Arch Gynecol Obstet [online] December, 281(5):895-900 [viewed 31 August 2014] Available from: doi:10.1007/s00404-009-1207-9
  5. OFOJEKWU M.J.N. et al. Hemoglobin and Serum Iron Concentrations in Menstruating Nulliparous Women in Jos, Nigeria. (2013) [online] LabMedicine, 44, 121-124. [viewed 31 August 2014] Available from: doi: 10.1309/LMM7A0F0QBXEYSSI & http://labmed.ascpjournals.org/content/44/2/121.short

Management - General Measures

Fact Explanation
Patient education Counseling and discussing the issues of menstruation with the female is necessary since each can have different issues, most of the times counseling could resolve the matters. [1, 2, 3, 4]
References
  1. FREDERICKS E. Short report: How family physicians can support discussions about menstrual issues Can Fam Physician [online] 2014 Mar, 60(3):e194-e196 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3952785
  2. O'FLYNN N. Menstrual symptoms: the importance of social factors in women's experiences Br J Gen Pract [online] 2006 Dec 1, 56(533):950-957 [viewed 31 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1934056
  3. CHAPPLE ALISON. Menorrhagia: women’s perceptions of this condition and its treatment. [online] 1999 June, 29(6):1500-1506 [viewed 31 August 2014] Available from: doi:10.1046/j.1365-2648.1999.01038.x
  4. KISSLING E. A.. Bleeding out Loud: Communication about Menstruation. Feminism & Psychology [online] 1996 November, 6(4):481-504 [viewed 31 August 2014] Available from: doi:10.1177/0959353596064002