Weinberg's Differential Rule Reconsidered

The study endeavored to assess the epidemiology, postnatal survival, and growth pattern of multiple births in Sub-Saharan Africa (SSA). It was based on the data of 25 demographic health surveys conducted in the subcontinent since 2008. The records of 213,889 children born in the preceding 59 months of the surveys were included. The multiple birth rate was computed as the number of multiple confinements per 1,000 births. Factors associated with multiple births were identified using logistic regression and their survival pattern was assessed using the Kaplan-Meier method. The multiple birth rate was 17.1 (95% confidence interval: 17.7-16.6) and showed considerable variation across the 25 countries included in the study. Odds of multiple births were significantly increased with advanced maternal age, parity, and maternal height but not with wealth index, age at first birth, and month of birth. At the end of the fourth year of age, the cumulative survival probability was as low as 0.77 in multiple births as compared to 0.93 in their counterparts. The odds of neonatal, infant and under-five mortality were 5.55, 4.39, and 3.72 times increased in multiple births, respectively. Multiple births tend to be malnourished than singletons and the odds of wasting, stunting, and underweight were 1.31, 1.83, and 1.73 times raised, consecutively. Nevertheless, multiple births regain their weight-for-age (WFA) and height-for-age (HFA) deficits by the end of the fourth year of age. Counseling pregnant mothers with multiple gestation to give birth at a health institution and providing close medical follow-up during and after the neonatal period can improve the survival of multiple births.

Section: Data Management and Analysismentioning

confidence: 99%

Multiple Births in Sub-Saharan Africa: Epidemiology, Postnatal Survival, and Growth Pattern

Gebremedhin

2014

“…Although the probability of a male birth is greater than .5, the reliability of the WDR's assumptions has never been conclusively verified or rejected (Fellman & Eriksson, 2006). According to WDR, the total number of DZ twin maternities is twice the number of twin maternities with opposite-sex (OS) twin sets.…”

Section: Estimation Of Mz and Dz Twinning Ratesmentioning

confidence: 99%

“…In addition, the erroneous variances are too small and may yield quite misleading test results and confidence intervals (CIs). Ford, the ratio between the correct variance estimate and the erroneous one (Fellman & Eriksson, 2006).…”

Section: Estimation Of Mz and Dz Twinning Ratesmentioning

confidence: 99%

Statistical Analyses of Monozygotic and Dizygotic Twinning Rates

Fellman

2013

Self Cite

The French mathematician Bertillon reasoned that the number of dizygotic (DZ) pairs would equal twice the number of twin pairs of unlike sexes. The remaining twin pairs in a sample would presumably be monozygotic (MZ). Weinberg restated this idea and the calculation has come to be known as Weinberg's differential rule (WDR). The keystone of WDR is that DZ twin pairs should be equally likely to be of the same or the opposite sex. Although the probability of a male birth is greater than .5, the reliability of WDR's assumptions has never been conclusively verified or rejected. Let the probability for an opposite-sex (OS) twin maternity be p O , for a same-sex (SS) twin maternity p S and, consequently, the probability for other maternities 1 − p S − p O . The parameter estimatesp O andp S are relative frequencies. Applying WDR, the MZ rate is m = p S − p O and the DZ rate is d = 2 p O , but the estimatesm andd are not relative frequencies. The maximum likelihood estimatorsp S andp O are unbiased, efficient, and asymptotically normal. The linear transformationsm =p S −p O andd = 2p O are efficient and asymptotically normal. If WDR holds they are also unbiased. For the tests of a set of m and d rates, contingency tables cannot be used. Alternative tests are presented and the models are applied on published data.

“…The practical importance of the rule is that if one has a sample of twin pairs of known sex combinations, one may thereby estimate the numbers of DZ and MZ pairs within the sample. Using external criteria, Fellman and Eriksson (2007) reported that (in spite of being apparently derived from a false premise) Weinberg's Differential Rule is nevertheless empirically correct to a close approximation. I inferred that if one makes the reasonable assumption that p is subject to Lexis variation across DZ twin births (comparable to that across singleton births), p must also be presumed to be subject to countervailing Poisson variation within DZ twin pairs (James, 2007).…”

Section: Poisson Variationmentioning

confidence: 99%

Sex Ratios in Twin Families: Commentary on Fellman and Eriksson

James¹

2008

Fellman and Eriksson (2008) wondered whether there is variation in the probability that a human birth will be male. Accordingly, they examined the sexes of sibs of index MM, MF, and FF twin pairs. For this purpose they used 19th century German data published by Geissler and Lommatsch. In these data, the sex ratio (proportion male at birth) of sibs of MM pairs was significantly high; while that of MF pairs was normal and that of FF pairs was significantly low (as contrasted with contemporaneous live birth sex ratios). Accordingly Fellman and Eriksson concluded that there is, indeed, variation across couples in the probability of producing a son. Here it will be noted that though there are external grounds supporting this conclusion, there is nevertheless some reason to suspect a form of systematic error in the data cited by these authors. (In Geissler's data, there is very substantial unexplained variation of sex ratio of the sibs preceding index twins by the sex and birth order of the twins). Both these points will be addressed here. In addition, evidence is adduced that (1) the sex ratio of MZ twins is low, and (2) the sex ratios of DZ twins and of their sibs are high. Lastly, appeals are made for (a) data that would test the reliability of the data of Geissler and Lommatsch on the point questioned above, and (b) data on the sex ratios of offspring of twins by the sex and zygosity of the twin parents.