The underlying mathematical techniques behind the multivariate normal distribution are explained in principle and expanded in detail for up to three variables. The application of multivariate distributions to screening programs is described with particular reference to the calculation of risk ratios for the detection of Down's syndrome between 15 and 19 weeks of gestation.
CuckleHSWaldNJThompsonSG. Estimating a woman's risk of having a pregnancy associated with Down's syndrome using her age and serum alpha-fetoprotein. Br J Obstet Gynae1987; 94: 387–402.
2.
PalomakiGEHaddowJE. Maternal serum alpha-fetoprotein, age and Down's syndrome risk. Am J Obstet Gynae1987; 156: 460–3.
3.
DiMaioMSBaumgartenAGreensteinRMSaalHMMahoneyMJ. Screening for fetal Down's syndrome in pregnancy by measuring maternal serum alpha-fetoprotein levels. New Engl J Med1987; 317: 342–6.
4.
WaldNJCuckleHSDensemJWMaternal serum screening for Down's syndrome in early pregnancy. BMJ1988; 297: 883–7.
5.
WhiteIPaphiaSSMagnayD.Improving methods of screening for Down's syndrome. New Engl J Med1989; 320: 401–2.
6.
DonnaiDAndrewsT.Screening for Down's syndrome: New methods allow detection of three fifths of affected pregnancies. BMJ1988; 297: 876.
7.
GillMMurdayVSlackJ.An economic appraisal of screening for Down's syndrome in pregnancy using maternal age and serum alpha fetoprotein concentration. Soc Sci Med1987; 24: 725–31.
8.
MerkatzIRNitowskyHMMacriJNJohnsonWE. An association between low maternal serum alpha fetoprotein and fetal chromosomal abnormalities. Am J Obstet Gynae1984; 148: 886–94.
9.
LockwoodCBenacerrafBKrinskyABlakemoreKBelangerKMahoneyMHobbinsJ.A sonographic screening method for Down syndrome. Am J Obstet Gynae1987; 157: 803–8.
10.
PerrellaRDuerinckxAJGrantEGTesslerFTabshKCrandallBF. Second trimester sonographic diagnosis of Down syndrome: Role of femur-length shortening and nuchal fold thickening. AJR1988; 151: 981–5.
11.
BenacerrafBGelmanRFrigolettoF.Sonographic identification of second trimester fetuses with Down's syndrome. New Engl J Med1987; 317: 1371–6.
12.
ToiASimpsonGFFillyRA. Ultrasonically evident fetal nuchal skin thickening: Is it specific for Down syndrome. Am J Obstet Gynae1987; 156: 150–3.
13.
FinkbeinerD.Introduction to Matrices and Linear Transformations, 2 edn.London: WH Freeman and Co1966; 100–11.
14.
MeyerP.Introductory Probability and Statistical Applications. 2nd edn.London: Addison-Wesley Publishing Co.1970; 198–201.
15.
JegerMEckmannB.Vector Geometry and Linear Algebra (for Engineers and Scientists). Bristol: Interscience publications; J Wiley and Sons Ltd1968; 107–55.
