TABLE 2.

Sample sizes of PISA studies used for linking study.

Domain	Study	Mode	N	#Items	#Link items
					All	Invariant
Science	2006	PBA	4881	103	77	56
	2009	PBA	3477	53	52	40
	2012	PBA	3505	52	52	40
	2014	PBA	340	91	77	56
	2014	CBA	338	91	77	56
	2015	CBA	6501	181	77	56
Mathematics	2003	PBA	4656	84	31	16
	2006	PBA	3795	48	31	16
	2009	PBA	3503	35	31	16
	2012	PBA	4971	84	66	36
	2014	PBA	345	70	66	36
	2014	CBA	340	68	66	36
	2015	CBA	2739	69	66	36
Reading	2000	PBA	5060	128	35	19
	2003	PBA	2555	27	24	13
	2006	PBA	2701	28	24	13
	2009	PBA	4975	100	82	47
	2012	PBA	3470	43	42	23
	2014	PBA	349	85	82	47
	2014	CBA	334	85	82	47
	2015	CBA	2746	87	82	47

Study = PISA study used. “2014” denotes the field test for PISA 2015, which was conducted in spring 2014. Mode = administration mode; PBA = paper-based assessment; CBA = computer-based assessment; N = sample size; #Items = number of items used in scaling model; #Link items = number of link items used in joint linking. The column “invariant” denotes the number of items that were declared to be invariant across CBA and PBA modes, according to the OECD (2017).