Table 1. The characteristics of the two study populations.

	CSi (N=23 632)						Horizon (N=3347)
	CSi-attenders (n=4865)		GP-attenders (n=4291)		Non-responders (n=14 476)		GP-taken sample (n=3347)
Mean age (years; 95% CI)	47.1	(46.8–47.5)	40.3	(40.0–40.6)	47.6	(47.4–47.8)	40.6	(40.3–41.0)
Age group (years)
27–29	385	7.9%	588	13.7%	1318	9.1%	478	14.3%
30–39	1092	22.4%	1657	38.6%	2962	20.5%	1295	38.7%
40–49	1215	25.0%	1311	30.6%	3107	21.5%	897	26.8%
50–59	1275	26.2%	514	12.0%	4099	28.3%	462	13.8%
60–65	898	18.5%	221	5.1%	2990	20.7%	215	6.4%
Total	4865	100.0%	4291	100.0%	14 476	100.0%	3347	100.0%
Screening historya
Long-term unscreened	1621	39.9%	927	30.8%	7540	64.0%	133	5.8%
Intermittently screened	2440	60.1%	2083	69.2%	4243	36.0%	2158	94.2%
Total	4061	100.0%	3010	100.0%	11 783	100.0%	2291	100.0%
Histology (regardless of the HPV test result)
Normal	134	47.3%	188	57.8%	47	78.3%	206	56.3%
CIN1	45	15.9%	30	9.2%	1	1.7%	44	12.0%
CIN2	22	7.8%	23	7.1%	0	0.0%	24	6.6%
CIN3	76	26.9%	76	23.4%	6	10.0%	61	16.7%
Cervical cancer	5	1.8%	7	2.2%	6	10.0%	1	0.3%
Inadequate material	1	0.4%	1	0.3%	0	0.0%	30	8.2%
Total	283	100.0%	325	100.0%	60	100.0%	366	100.0%
⩾CIN2 detection (regardless of the HPV test result)
<CIN2	179	63.5%	218	67.3%	48	80.0%	250	74.4%
⩾CIN2 (positive predictive value)	103	36.5%	106	32.7%	12	20.0%	86	25.6%
Total	282	100.0%	324	100.0%	60	100.0%	336	100.0%
Positive predictive value of ⩾CIN2 detection compared with Horizon	P<0.01		P=0.02		P=0.93		Reference

Abbreviations: CI=confidence interval; CIN=cervical intraepithelial neoplasia; GP=general practitioner; HPV=human papillomavirus; Intermittently screened=cytology sample registered within the past 10 years (though not in the last screening round, see eligibility criteria); Long-term unscreened=no cytology sample registered in the past 10 years.

^aRestricted to women aged ⩾34 years, N=21 145 for both studies combined. These women have been recommended for screening for at least 10 years.