Evaluating Precision of a Trachomatous Trichiasis (TT) Super Survey with Modulating Sample Sizes in Tanzania

Figures & data

Table 1. Baseline TT survey results.

Scenario	District	Year	TF prevalence (%) (95% CI)	TT prevalence (%) (95% CI)
Opportunity 1	Babati DC	2012	0.3 (0.1–0.6)	0.55 (0.13–1.18)
	Mbulu DC	2012	2.8 (1.1–4.5)	0.80 (0.12–1.70)
Opportunity 2	Iringa DC/ Kilolo DC*	2004	<5	0.91 (0.44–1.56)
	Mufindi DC	2014	0.3 (0.1–0.6)	0.35 (0.14–0.63)

*In 2004 these two districts were a single district and surveyed as such. They were divided into two districts in 2014. The 2004 TF estimates have not been published and so the value presented here is from the available categorical data from the global atlas of trachoma (https://www.trachomaatlas.org).

Figure 1. Distribution of first-stage village data points in Babati DC and Mbulu DC.

Figure 2. Distribution of first-stage village data points in Iringa DC, Kilolo DC, and Mufindi DC.

Table 2. Opportunity 1, 2018 unknown to the health system prevalence estimates.

District	TT prevalence unknown to the health system	Standard Error	95% CI (lower)	95% CI (upper)
Babati DC	0.27%	0.17%	0.01%	0.65%
Mbulu DC	0.20%	0.17%	0.00%	0.57%
Super EU	0.24%	0.12%	0.03%	0.50%

Figure 3. Opportunity 1 distribution of super EU unknown to the health system bootstrap results with modulating sample sizes. Dashed lines represent 95% confidence intervals and the red dashed lines represent the mean; solid lines represent the elimination threshold of 0.2%.

Table 3. Opportunity 1, 2018 super EU unknown to the health system prevalence estimates with modulating sample sizes.

Sample size		TT prevalence	Standard Error	95% CI (lower)	95% CI (upper)
Number of villages	Percent of total villages
60	100%	0.24%	0.12%	0.03%	0.50%
54	90%	0.24%	0.13%	0.02%	0.52%
48	80%	0.24%	0.13%	0.02%	0.52%

The confidence intervals for the 80% simulation are wider than the 90% simulation, due to the third decimal place in the lower bound.

Table 4. Opportunity 2, 2018 prevalence estimates.

	Unknown to the health system				All cases
District	TT prevalence	Standard Error	95% CI (lower)	95% CI (upper)	TT prevalence	Standard Error	95% CI (lower)	95% CI (upper)
Iringa DC	0.30%	0.10%	0.13%	0.51%	0.33%	0.10%	0.16%	0.54%
Kilolo DC	0.15%	0.13%	0.00%	0.43%	0.15%	0.13%	0.00%	0.44%
Mufindi DC	0.15%	0.08%	0.03%	0.32%	0.19%	0.08%	0.05%	0.37%
Super EU	0.20%	0.06%	0.10%	0.33%	0.23%	0.06%	0.12%	0.35%

Figure 4. Opportunity 2 distribution of super EU unknown to the health system bootstrap results with modulating sample sizes. Dashed lines represent 95% confidence intervals and the red dashed lines represent the mean; solid lines represent the elimination threshold of 0.2%.

Table 5. Opportunity 2 super EU prevalence estimates with modulating sample sizes.

Sample size		TT prevalence	Standard Error	95% CI (lower)	95% CI (upper)
Number of villages	Percent of total villages
90	100%	0.20%	0.06%	0.10%	0.33%
81	90%	0.24%	0.11%	0.06%	0.47%
74	80%	0.24%	0.11%	0.05%	0.48%