Table 6. Missing data on nhs number or postcode by data year.

		1998–2003 (n = 99,200)			2004–2009 (n = 128,666)			2010–2015 (n = 189,373)
	n	NHS number (%)	Postcode (%)	n	NHS number (%)	Postcode (%)	n	NHS number (%)	Postcode (%)
% missing
Age
0–3	68,225	61.2	19.0	77,270	6.5	41.3	89,896	0.7	47.3
4–7	17,774	17.5	2.6	13,112	4.5	2.9	13,435	1.7	2.8
8–11	13,221	10.8	4.0	11,833	4.4	4.1	10,309	1.2	2.0
12–15				15,370	4.7	4.0	14,144	1.5	3.7
16–19				11,081	3.4	3.8	24,304	1.9	4.0
20–23							37,285	1.8	3.9
Sex
Missing	278	46.8	10.4	27	59.3	37.0	45	6.7	24.4
Male	43,996	48.7	15.2	60,181	5.9	27.3	99,675	1.1	22.8
Female	54,946	45.0	13.1	68,458	5.3	25.4	89,653	1.4	26.0
Ethnic group
Missing	51,188	52.9	16.2	26,669	7.9	36.4	17,133	3.1	21.0
White	40,263	37.8	12.0	83,078	4.6	22.4	137,015	0.8	23.5
Mixed	142	16.9	2.8	2,698	5.5	27.2	6,078	1.2	34.0
Asian	3,399	42.1	8.6	8,812	6.0	28.2	15,461	1.5	29.8
Black	1,807	55.0	6.9	4,804	7.9	31.1	8,029	1.9	26.3
Chinese/Other	2,421	62.4	17.1	2,605	10.1	30.2	5,657	3.8	25.8
Socio-economic group
Missing	13,937	65.7		33,808	6.7		46,042	0.7
Low deprivation	59,914	43.5		67,485	4.8		100,721	1.0
High deprivation	25,122	43.2		26,851	5.0		41,600	1.3
Foreign	236	80.9		401	81.0		862	53.8
No fixed abode	11	45.5		121	20.7		148	12.8