... bias

Appendices B, C and D are available in electronic form only, at http://www.edpsciences.org

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... selection

The only exception is VLA J123642+6213 (Waddington et al. 1999), which has been identified in the HDF, but it does have a steep spectral index ( $\alpha_{1400}^{8500}=-0.94$).

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... sky

To facilitate optical follow-up, we will exclude the Galactic plane at |b|<15$^\circ$.

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... excluded

This also reduces the number of Galactic pulsars in our sample (see Sect. 4.7.2).

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...$\alpha_{365}^{1400} < -1.30$sources

Only due to the spectral index cutoff, the sample has more important incompleteness factors; see Sect. 2.2.

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... correlations

The TN sample will have more spurious sources at low flux density levels; see Sect. 2.2.

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... index

In the Westerbork faint USS (Wieringa & Katgert 1992) or the USS sample from Röttgering et al. (1994), there is also a decrease in the identification fraction, even at limiting magnitudes of R=22.5 and R=23.7, indicating that this trend continues out to fainter magnitudes and radio fluxes.

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... clusters

In the RASS-BSC, only 14% of the extra-galactic sources are identified with galaxy clusters (Voges et al. 1999).

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