Net selectivity is the remaining selectivity after deducting the amount of return require to justify not being fully diversified
Details
If net selectivity is negative the portfolio manager has not justified the loss of diversification
$$Net selectivity = \alpha - d$$
where \(\alpha\) is the selectivity and \(d\) is the diversification
References
Carl Bacon, Practical portfolio performance measurement and attribution, second edition 2008 p.78
Examples
data(portfolio_bacon)
print(NetSelectivity(portfolio_bacon[,1], portfolio_bacon[,2])) #expected -0.017
#> portfolio.monthly.return....
#> portfolio.monthly.return.... -0.0178912
data(managers)
print(NetSelectivity(managers['1996',1], managers['1996',8]))
#> HAM1
#> HAM1 0.01333906
print(NetSelectivity(managers['1996',1:5], managers['1996',8]))
#> HAM1 HAM2 HAM3 HAM4 HAM5
#> Net Selectivity (Risk free = 0) 0.01333906 NA 0.1745397 -0.03249043 NA