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Table 1 Covariates included in constrained randomisation

From: The AWED trial (Applying Wolbachia to Eliminate Dengue) to assess the efficacy of Wolbachia-infected mosquito deployments to reduce dengue incidence in Yogyakarta, Indonesia: study protocol for a cluster randomised controlled trial

Category

Covariate

Rationale

Balancing criterion

Potential confounders

1. Age: % of population < 15 yearsa

Dengue risk is age dependent

Each arm within ± 5% of overall population value

2. 3-year average dengue incidence ratea

Historical dengue incidence may predict future risk

Each arm within ± 5% of overall population value

3. Education: % completed high schoola

Proxy for socioeconomic status that may predict dengue risk

Each arm within ± 5% of overall population value

Potential sources of bias

4. Incidence of other febrile illnessf presenting to Puskesmas clinics in 2014–2015b

Prevent chance association between other febrile illness and intervention

Each arm within ± 5% of overall population value

Sample size

5. Number of clusters

To maximise precision and power

12 clusters per study arm

 

6. Cluster populationc

To maximise precision and power

Each arm 45–55% of total population

Logistics

7. Total cluster area (km2)d

Releases to be done over approximately half the city

Each arm 45–55% of total area

 

8. Non-release area within cluster (km2)e

To prevent an excess of non-residential areas falling in intervention arm

Each arm 45–55% of total non-release area

 

9. Four spatial strata

To prevent a large contiguous intervention area

Within each spatial stratum, three clusters per study arm

  1. Data sources: aYogyakarta and Bantul District Health Offices; bRecords from individual primary health clinics (Puskesmas); cStatistics Indonesia (BPS), 2015; dCalculated in ArcGIS; eCalculated in ArcGIS and Google Earth.
  2. fOther febrile illness extracted based on ICD10 codes R50 (Fever of other and unknown origin), R50.9 (Fever, unspecified), A75.9 (Typhus fever, unspecified), A49 (staphylococcal infection, unspecified site)