Table 1.

Classification and Nomenclature of the Investigated Anchor Methods.

Anchor class	Anchor selection	Combination	Initial step and anchor selection strategy
All-other	None	All-other	Initial step: Each item is tested for DIF using all remaining items as anchor.
		Cf. for example, Woods (2009)	Selection strategy: No additional selection strategy is required.
Constant	AO	Single- anchor-AO	Initial step: Each item is tested for DIF using all remaining items as anchor.
		Woods (2009)	Selection strategy: The item with the lowest absolute DIF statistic (AO) is chosen.
	SA	Single- anchor-SA	Initial step: Each item is tested for DIF using every other item as single-anchor.
		Wang (2004)	Selection strategy: The item with the smallest number of significant DIF tests (SA) is chosen.
	AO	Four-anchor-AO	Initial step: Each item is tested for DIF using all remaining items as anchor.
		Woods (2009); Wang, Shih, and Sun (2012)	Selection strategy: The four anchor items corresponding to the lowest ranks of the absolute DIF statistics from the initial step (AO) are chosen.
	SA	Four-anchor-SA	Initial step: Each item is tested for DIF using every other item as single-anchor.
		Wang (2004)	Selection strategy: The four-anchor items corresponding to the smallest number of significant DIF tests (SA) are chosen.
	NC	Four-anchor-NC	Initial step: Each item is tested for DIF using every other item as single-anchor.
		Proposed by Wang (2004)	Selection strategy: The first anchor is found as in single-anchor-SA; the next candidate anchor item (up to three) is found from tests using the current anchor if its result corresponds to the lowest non-significant absolute test statistic and is then added to the current anchor.
Iterative backward	AO	Iterative-backward-AO	Initial step: Each item is tested for DIF using all remaining items as anchor.
		For example, Drasgow (1987)	Selection strategy: Iteratively, all items displaying DIF are excluded from the anchor and the next DIF test with the current anchor is conducted.
Iterative forward	AO	Iterative-forward-AO	Initial step: Each item is tested for DIF using all remaining items as anchor.
			Selection strategy: As long as the current anchor is shorter than the number of currently presumed DIF-free items, the next item with the lowest rank in the initial step (AO) is added to the anchor.
	SA	Iterative-forward-SA	Initial step: Each item is tested for DIF using every other item as single-anchor.
			Selection strategy: As long as the current anchor is shorter than the number of currently presumed DIF-free items, the next item with the smallest number of significant test results in the initial step (SA) is added to the anchor.

Note. DIF = differential item functioning; AO = all-other selection; SA = single-anchor selection; NC = next candidate selection.