. 2011 Dec 12;67B(1):121–132. doi: 10.1093/geronb/gbr133

Table 2.

Comparisons Between Surveys of Original and DIF-Adjusted IRT Scores Reflecting Mean Disability

	Original			DIF adjusted			N
	HRS	ELSA	SHARE	HRS	ELSA	SHARE	HRS	ELSA	SHARE
Total	1.09^a^,^b	.81^a^,^c	.68^b^,^c	1.70^a^,^b	1.46^a^,^c	1.17^b^,^c	10,905	5,437	13,408
Age
65–74	0.55^b	0.59^c	0.31^b^,^c	0.99^a^,^b	1.10^a^,^c	0.63^b^,^c	5,879	3,152	8,022
75–84	1.17^a^,^b	0.96^a	0.92^b	1.90^a^,^b	1.75^a^,^c	1.59^b^,^c	3,668	1,859	4,390
85+	3.17^a^,^b	1.80^a^,^c	2.55^b^,^c	4.24^a^,^b	2.96^a^,^c	3.66^b^,^c	1,358	426	996
Gender
Men	0.85^a^,^b	0.72^a^,^c	0.53^b^,^c	1.39^b	1.30^c	0.93^b^,^c	4,620	2,423	6,070
Women	1.26^a^,^b	0.89^a^,^c	0.80^b^,^c	1.93^a^,^b	1.60^a^,^c	1.36^b^,^c	6,285	30,140	7,338
Men
65–74	0.52^b	0.54^c	0.28^b^,^c	0.93^b	1.01^c	0.55^b^,^c	2,678	1,462	3,805
75–84	1.00^b	0.85	0.75^b	1.65^b	1.53^c	1.33^b^,^c	1,503	792	1,929
85+	2.37^a	1.67^a	2.07	3.29^a	2.67^a	2.90	439	171	336
Women
65–74	0.57^b	0.64^c	0.34^b^,^c	1.05^b	1.17^c	0.70^b^,^c	3,201	1,692	4,217
75–84	1.29^a^,^b	1.04^a	1.06^b	2.07^b	1.91	1.79^b	2,165	1,067	2,461
85+	3.55^a^,^b	1.89^a^,^c	2.80^b^,^c	4.69^a^,^b	3.16^a^,^c	3.99^b^,^c	919	255	660
Education^d
Secondary/high school or less	1.26^a^,^b	0.90^a^,^c	0.72^b^,^c	1.95^a^,^b	1.59^a^,^c	1.24^b^,^c	7,197	4,070	11,548
Beyond secondary/high school	0.74^a^,^b	0.49^a^,^c	0.38^b^,^c	1.22^a^,^b	0.96^a^,^c	0.73^b^,^c	3,705	843	1,744

Notes. ADL = activities of daily living; DIF = differential item functioning; ELSA = English Longitudinal Study of Aging; HRS = Health and Retirement Survey; IADL = instrumental activities of daily living; IRT = item response theory; SHARE = Survey of Health, Ageing and Retirement in Europe; Original scores = sum of 11 ADL and IADL items where difficulty was reported; DIF-adjusted IRT scores = linear transformation of DIF-adjusted IRT scores so that range = 0–11.

HRS and ELSA different at p ≤ .05.

HRS and SHARE different at p ≤ .05.

ELSA and SHARE different at p ≤ .05.

Missing cases in Education due to Don’t Know responses or inability to classify; 3 in HRS; 524 in ELSA (mostly in a “foreign education category” that could not be classified); 116 in SHARE.