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Table 3 Sample sizes for a controlled intervention study with Composite Referral Completion Indicator (CRCI) as the outcome measure, based on England and Wales population structure a

From: Development of a composite outcome score for a complex intervention - measuring the impact of Community Health Workers

Level of similarity within households in disease risk factors/level of similarly within households in level of compliance of uptake of interventions Intervention percentage effect Mean (SD) CRCI in control arm Mean (SD) CRCI in CHW arm Sample size number of households per arm based on comparison of mean CRCIs, allowing for inclusion of householdsbwithout valid CRCI:
Without clustering of intervention by region With clustering of intervention by regions of 100 households, Intra-CHW ICC = 0.01 With clustering of intervention by regions of 100 households, Intra-CHW ICC = 0.02 With clustering of intervention by regions of 100 households, Intra-CHW ICC = 0.05
Typical distribution across England and Wales: none/none 10% 0.56 (0.36) 0.61 (0.36) 1,650 3,280 4,920 9,820
none/none 20% 0.56 (0.36) 0.65 (0.35) 400 800 1,190 2,380
none/none 30% 0.56 (0.36) 0.69 (0.34) 170 340 510 1,010
none/high 10% 0.56 (0.41) 0.61 (0.39) 1,970 3,920 5,870 11,720
none/high 20% 0.56 (0.41) 0.65 (0.38) 490 980 1,460 2,920
none/high 30% 0.56 (0.41) 0.69 (0.36) 210 420 630 1,250
high/none 10% 0.6 (0.37) 0.64 (0.36) 1,990 3,960 5,930 11,840
high/none 20% 0.6 (0.37) 0.68 (0.35) 490 980 1,460 2,920
high/none 30% 0.6 (0.37) 0.72 (0.33) 210 420 630 1,250
high/high 10% 0.6 (0.41) 0.64 (0.39) 2,470 4,920 7,360 14,700
high/high 20% 0.6 (0.41) 0.68 (0.38) 590 1,170 1,760 3,510
high/high 30% 0.6 (0.41) 0.72 (0.36) 250 500 750 1,490
Typical distribution of deprived areas none/none 10% 0.57 (0.36) 0.61 (0.35) 1,650 3,280 4,920 9,820
none/none 20% 0.57 (0.36) 0.66 (0.34) 400 800 1,190 2,380
none/none 30% 0.57 (0.36) 0.7 (0.33) 170 340 510 1,010
none/high 10% 0.57 (0.4) 0.62 (0.39) 1,970 3,920 5,870 11,720
none/high 20% 0.57 (0.4) 0.66 (0.37) 480 960 1,430 2,860
none/high 30% 0.57 (0.4) 0.7 (0.36) 210 420 630 1,250
high/none 10% 0.6 (0.36) 0.64 (0.35) 2,010 4,000 5,990 11,960
high/none 20% 0.6 (0.36) 0.68 (0.34) 480 960 1,430 2,860
high/none 30% 0.6 (0.36) 0.72 (0.33) 210 420 630 1,250
high/high 10% 0.6 (0.4) 0.64 (0.39) 2,400 4,780 7,150 14,280
high/high 20% 0.6 (0.4) 0.68 (0.37) 580 1,150 1,730 3,450
high/high 30% 0.6 (0.4) 0.72 (0.35) 250 500 750 1,490
  1. a(Excluding chlamydia) and based on 90% power at 5% significance level. b88.3% of households have valid CRCI with no intra-household correlation of disease risk factors, and 84.8% of households have valid CRCI based on high intra-household correlation of disease risk factors. Intervention percentage effect is proportion of services (immunisations/screening tests, stop-smoking clinics) that are taken up with CHW intervention, out of those services that would not otherwise be taken up.
  2. Abbreviations: CHW Community Health Worker, ICC intra-class correlation coefficient.