Constructing second-order accurate confidence intervals for communalities in factor analysis.

In an effort to find accurate alternatives to the usual confidence intervals based on normal approximations, this paper compares four methods of generating second-order accurate confidence intervals for non-standardized and standardized communalities in exploratory factor analysis under the normality assumption. The methods to generate the intervals employ, respectively, the Cornish-Fisher expansion and the approximate bootstrap confidence (ABC), and the bootstrap-t and the bias-corrected and accelerated bootstrap (BC(a)). The former two are analytical and the latter two are numerical. Explicit expressions of the asymptotic bias and skewness of the communality estimators, used in the analytical methods, are derived. A Monte Carlo experiment reveals that the performance of central intervals based on normal approximations is a consequence of imbalance of miscoverage on the left- and right-hand sides. The second-order accurate intervals do not require symmetry around the point estimates of the usual intervals and achieve better balance, even when the sample size is not large. The behaviours of the second-order accurate intervals were similar to each other, particularly for large sample sizes, and no method performed consistently better than the others.

Concentrations of organochlorine pollutants in mothers who gave birth to neonates with congenital hypothyroidism.

We have investigated the effects of prenatal exposure to dioxin-like compounds (PCDDs, PCDFs and dioxin-like PCBs), PCBs and organochlorine pesticides (DDT, HCH, chlordane, HCB and their metabolites) on the incidence of congenital hypothyroidism and/or cretinism in Fukuoka, Japan from 2001 to 2004. Thirty-four positive neonates of the mass-screening for cretinism were classified into three groups by the pediatrician after the reevaluation of the serum TSH level, that is, negative in reevaluation group, hyper thyroid stimulating hormone (TSH) emia group and cretinism group. One-hundred and two negative neonates of the mass-screening were classified into the normal group. Concentrations of these organochlorine compounds in the breast milk of mothers, which were considered as the indicator of prenatal exposures to them, were gradually increased from the normal group to the cretinism group in the four groups and were around two times higher in the cretinism group than in the normal group. According to the case-control study adjusted for the parity and mother's age, odds ratios of PCBs, DDT and HCB were 10 (p=0.003), 10 (p=0.003) and 22 (p=0.004), respectively and in dioxin-like compounds, PCDFs showed the highest odds ratio, 9.8 (p=0.005). Based upon those findings, these compounds seemed play an important role in the incidence and/or causation of the cretinism.