Source Evaluation and Trace Metal Contamination in Benthic Sediments from Equatorial Ecosystems Using Multivariate Statistical Techniques

race metals (Cd, Cr, Cu, Ni and Pb) concentrations in benthic sediments were analyzed through multi-step fractionation scheme to assess the levels and sources of contamination in estuarine, riverine and freshwater ecosystems in Niger Delta (Nigeria). The degree of contamination was assessed using the individual contamination factors (ICF) and global contamination factor (GCF). Multivariate statistical approaches including principal component analysis (PCA), cluster analysis and correlation test were employed to evaluate the interrelationships and associated sources of contamination. The spatial distribution of metal concentrations followed the pattern Pb>Cu>Cr>Cd>Ni. Ecological risk index by ICF showed significant potential mobility and bioavailability for Cu, Cu and Ni. The ICF contamination trend in the benthic sediments at all studied sites was Cu>Cr>Ni>Cd>Pb. The principal component and agglomerative clustering analyses indicate that trace metals contamination in the ecosystems was influenced by multiple pollution sources

Statistical inference procedure for the mean–variance efficient frontier with estimated parameters

Mean–variance analysis, Efficient frontier, Multivariate test, Parameter uncertainty, Exact distribution,

A Test of a Buying Rule for "Underpriced" Apartment Buildings

Apartment-building repeat-sales data are used to test a trading rule. Property values are estimated through regression; if the actual price is less than the estimated value, the property may be "undervalued." Returns are calculated for these "undervalued" properties and adjusted for risk using the Sharpe ratio. A test is done of whether these ratios are significantly different for different portfolios. The "undervalued" properties have higher appreciation returns, but once these are adjusted for risk, the differences in returns are not significant. The paper contributes to the real estate efficiency literature and suggests a workable method for comparing the performance of real estate portfolios on a risk-adjusted basis. Copyright American Real Estate and Urban Economics Association.

Comparison of different estimation techniques for portfolio selection

Portfolio analysis, Mean-variance analysis, Estimation of portfolio weights, Shrinkage estimation,